What Am I Looking At?

It separates the upper lip scales of the left and right sides.

Why people look at it: Its shape can help: some species have a long rostral, or one with a very distinctive shape.

Other names: rostral scale, rostral plate

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Rostral: The single enlarged plate at the tip of the snout (fig. 6).”

“Rostral – The scale at the very anterior tip of the upper lip. It separates the upper labials on one side of the head from the other. […] However, some species have an elongate rostral that extends beyond the lower jaw and/or has a very distinctive shape.”

It may be single, partly divided, or fully divided into a prenasal and a postnasal by a seam running through the nostril.

Why people look at it: Whether the nasal is single, partly divided or fully divided is a character in some keys.

Other names: nasal scale, nasal shield

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Nasal: The scale enclosing the nostril; may be single, partially divided (by a suture extending down from the nostril), or completely divided (giving a pre- and postnasal) by a vertical suture that extends through the nostril (fig. 6).”

“Nasal Divided/Single/Semi-divided – The nasal is semi-divided if the nostril connects to one edge of the nasal. It is fully divided if the nostril connects to two edges of the scale, effectively splitting the nasal into two scales.”

Other names: anterior nasal

Sources: Nasal scale (Wikipedia); Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Sometimes this scale is paired (divided). In such cases, the anterior half is referred to as the prenasal and the posterior half is referred to as the postnasal.”

The loreal lies behind it.

Other names: posterior nasal

Sources: Nasal scale (Wikipedia); Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Sometimes this scale is paired (divided). In such cases, the anterior half is referred to as the prenasal and the posterior half is referred to as the postnasal.”

“Loreal: The scale on the side of the head lying between the (post-) nasal and the preocular(s)”

The nasal can be single, partly divided, or divided by a seam through the nostril, so how the nostril sits among the scales differs between snakes.

Some sources give a simple rule for where the nostril sits in different families; it rests on a weak citation, so we leave it out.

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Nasal: The scale enclosing the nostril; may be single, partially divided (by a suture extending down from the nostril), or completely divided (giving a pre- and postnasal) by a vertical suture that extends through the nostril (fig. 6).”

The loreal scale is not the same thing as the loreal pit of pitvipers.

Why people look at it: Keys ask whether it is there: some snakes lack it, and some have more than one.

Other names: loreal scale, loreal shield

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.); Timber Rattlesnake (Crotalus horridus) (Virginia Herpetological Society)

“Loreal: The scale on the side of the head lying between the (post-) nasal and the preocular(s)”

“Loreal – The scale(s) between the preocular(s) and the nasal scale. It is sometimes absent.”

“loreal scales 1-3, but usually 2”

It lies in the loreal region; it is not the loreal scale.

Why people look at it: The Navy manual calls the pits heat receptors that help the snake find prey in the dark, and says they identify a snake as a pitviper, while noting that some pythons and boas have pits on the upper lip. Head markings often hide the pits, so they can be hard to see: use a clear photo, and never get close to a snake to look.

Other names: pit, facial pit, heat-sensing pit, pit organ

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Prairie Rattlesnakes (National Park Service)

“Pit (or Loreal Pit): The deep depressions on the side of the head in the loreal region in pit vipers (family Crotalidae); they are heat-sensitive and aid the snake in finding its prey in the dark (fig. 4).”

“In all pit vipers (family Crotalidae) there is a deep hollow between the eye and nostril and slightly below a line connecting the two (see figure 4). […] These pits are actually sensitive heat receptors. They absolutely identify a snake as a pit viper, since they are not seen in any other type of snake. However, some pythons and boas do have pits on the upper lip. The pits may be difficult to recognize for they are often camouflaged by the head markings so that they are not visible except by close inspection”

“The facial pit is present in all rattlesnakes (see fig. 4 p. 26).”

“These snakes have a heat-sensitive pit on each side of their head between the nostril and the eye.”

Other names: preocular scale

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.); Timber Rattlesnake (Crotalus horridus) (Virginia Herpetological Society)

“Preoculars: The scale(s) lying immediately in front of and in contact with the eye (fig. 6).”

“preoculars 1-2 on each side”

Other names: postocular scales

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Postoculars: The scale(s) immediately behind and in contact with the eye. Usually between the supralabials and the supraoculars (fig. 6).”

Other names: subocular scales

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Suboculars: The scale(s) immediately below and in contact with the eye; between the eye and the supralabials (fig. 6).”

It separates the eye from the frontal.

Other names: supraocular scale, supraocular plate

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Supraoculars: The enlarged scales or scutes (sometimes divided) on the crown directly above each eye (fig. 6).”

“Supraoculars – The scale(s) directly above the eye. Typically one on each side of the head, they separate the eye from the frontal.”

The front row touches the postoculars; the rows behind it do not.

Other names: temporal scales

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Temporals: Scales or scutes on the side of the head between the parietals and the supralabials, and behind the postoculars; anterior temporal(s) are in contact with the postoculars; posterior (sometimes secondary and tertiary) temporals are in vertical rows, not in contact with postoculars (fig. 6).”

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“anterior temporal(s) are in contact with the postoculars”

“Anterior temporals – The scale(s) immediately posterior to the postocular(s). They separate the upper labials from the parietals. There are usually one or two but there can be up to four, or none at all.”

Other names: secondary temporals, tertiary temporals

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“posterior (sometimes secondary and tertiary) temporals are in vertical rows, not in contact with postoculars (fig. 6).”

To count them, leave out the rostral, stop at the corner of the mouth, and count one side.

Why people look at it: Species accounts give a count for each side: the Virginia account of the Northern Watersnake gives 8/8 for most animals.

Other names: upper labials, upper lip scales

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.); Northern Watersnake (Nerodia sipedon sipedon) (Virginia Herpetological Society); Timber Rattlesnake (Crotalus horridus) (Virginia Herpetological Society)

“Supralabials: The scales (usually enlarged) or scutes along the border of the upper lip behind the rostral (fig. 6).”

“Upper labials – The scales along the upper lip of the snake's mouth. Do not count the very front scale (the rostral) and stop counting at the corner of the mouth. Only count one side of the head.”

“supralabials 8/8 (88.6%, n = 326)”

“supralabials 13/14 (32.1%, n = 81) […] or other combinations of 11-15 (14.8%)”

To count them, leave out the mental, stop at the corner of the mouth, and count one side.

Other names: lower labials, lower lip scales

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.); Timber Rattlesnake (Crotalus horridus) (Virginia Herpetological Society)

“Infralabials: The (usually enlarged) scales along the border of the lower lip behind the mental (fig. 6).”

“Lower labials – The scales along the lower lip of the snake's mouth. Do not count the very front scale (the symphysial) and stop counting at the corner of the mouth. Do not count both sides of the head.”

“infralabials 15/15 (20.3%, n = 79) […] or other combinations of 12-16 (31.6%)”

It may be sharp, blunt, barely there, or absent.

Other names: canthus rostralis

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Canthus (or canthus rostralis): The angle between the flat crown of the head and the side, between snout and eye; may be sharp, obtuse, obsolete, or absent.”

Other names: canthals

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Canthal scales: Enlarged scales along the lateral border of the crown between internasals and supraoculars in some vipers and pit vipers (fig. 12).”

They separate the nasal scales of the two sides.

Other names: internasal scales

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Internasal(s): The (usually paired) scutes on the crown just behind the rostral (fig. 6).”

“Internasals – The scales that separate the nasal scales from each other. They are immediately posterior to the rostral. They are usually paired and symmetrical but there can be just one single scale or they can be absent all together.”

Other names: prefrontal scales

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Prefrontal(s): The (usually paired) enlarged scutes just behind the internasals, or that area if it is covered with small scales (fig. 6).”

“Prefrontals – The scale(s) immediately posterior to the internasal(s). They are usually paired and symmetrical but sometime there is only a single scale.”

Other names: frontal scale, frontal shield

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Frontal: The single enlarged median scute on the crown between the supraoculars and behind the prefrontals (fig. 6).”

Other names: parietal scales, parietal shields

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Parietals: The large paired scutes at the rear end of the crown, immediately behind the frontal and supraoculars (fig. 6).”

In most snakes it is covered by large, symmetrical plates (shields), each with its own name. In many vipers, boas and pythons these plates are broken up, more or less, into small scales.

Why people look at it: The Navy manual calls the size and arrangement of the shields on the top and sides of the head most helpful in snake identification.

Other names: crown shields, head shields

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snake scale (Wikipedia)

“The size and arrangement of shields on the top and sides of the head are most helpful in snake identification. In the great majority of snakes the top of the head is covered by large symmetrical shields, typically 9 in number (see fig. 6). More or less division of these shields into small scales is seen in many kinds of vipers, many boas and pythons, and in a few other kinds of snakes.”

Rattlesnakes of the genus Sistrurus, such as the Pygmy Rattlesnake, have large crown plates, as do most Agkistrodon.

Why people look at it: The Navy manual's key to North American pitvipers uses it: nine large crown shields lead to Sistrurus; small or broken-up crown scales lead to Crotalus.

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Timber Rattlesnake (Tennessee Wildlife Resources Agency)

“Nine large crown shields are seen in rattlesnakes of the genus Sistrurus. In the genus Crotalus the crown shields are more or less extensively fragmented.”

“[Crotalus] Head scales: Supraoculars present, a pair of internasals often distinct, occasionally a pair of prefrontals; enlarged canthal scales often present; other parts of crown covered with small scales.”

“[Agkistrodon] Head scales: The usual 9 on the crown in most species”

“The Pygmy Rattlesnake is much smaller with a tiny rattle; the crown of the head has 9 large plates (instead of small scales).”

“6. A. Nine large shields on crown … Sistrurus B. Crown shields small or fragmented into scales … Crotalus”

Other names: symphysial, mental scale

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); THE FAUNA OF BRITISH INDIA, CEYLON AND BURMA, INCLUDING THE WHOLE OF THE INDO-CHINESE SUB-REGION. REPTILIA and AMPHIBIA. VOL. III.—SERPENTES. (BY MALCOLM A. SMITH; Originally published, 1943 (scan is the 1981 Indian reprint))

“Mental: The triangular scale at the symphysis of the lower jaw, corresponding in position to the rostral of the upper jaw (fig. 6).”

“m, mental (or symphysial)”

They touch the mental, or are separated from it by the first lower lip scales.

Other names: anterior genials, genials, chin shields

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Chin shields (Genials): Paired enlarged scales near the ventral midline of the lower jaw; anterior chin shields in contact with mental or separated from it by first infralabials; a pair of posterior chin shields may be present behind the anterior (fig. 6).”

“There are usually two pairs of chin shields, but 1 or 3 pairs can also be found in some species. […] The first pair of chin shields is often separated from the symphysial by the first pair of infralabials.”

Other names: posterior genials

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); THE FAUNA OF BRITISH INDIA, CEYLON AND BURMA, INCLUDING THE WHOLE OF THE INDO-CHINESE SUB-REGION. REPTILIA and AMPHIBIA. VOL. III.—SERPENTES. (BY MALCOLM A. SMITH; Originally published, 1943 (scan is the 1981 Indian reprint))

“a pair of posterior chin shields may be present behind the anterior (fig. 6).”

“pg, posterior genials (or chin shields)”

Most snakes have one, running between the paired chin shields and on between the smaller throat scales (gulars).

Our only sources for this term are encyclopedia entries.

Sources: Mental groove (Wikipedia); Snake scale (Wikipedia)

“Most snakes have a longitudinal groove on the underside of the head between large, paired chin shields and smaller gular scales. This is referred to as Mental groove.”

“The mental groove is a longitudinal groove on the underside of the head between the large, paired chin shields and continuing between the smaller gular scales.”

Why people look at it: Near the head, rows of gulars push in at the edges of the belly plates, which is why the first belly plate is hard to pick out without a rule (see First ventral).

Other names: gular scales, throat scales

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); A PROPOSED STANDARD SYSTEM OF COUNTING VENTRALS IN SNAKES (By HERNDON G. DOWLING, University of Michigan Museum of Zoology, Ann Arbor, Michigan; British Journal of Herpetology Vol. 1, No. 5, November, 1951)

“Gulars: The rows of small nonspecialized scales on the ventral surface of the lower jaw anterior to the ventral plates (fig. 6).”

“In the head region, however, scale rows from the chin and throat (gulars) begin to invade the lateral edges of the ventral row, and as more gular rows are added the ventrals become smaller and smaller until often they approximate the size of the gular rows before reaching the chin shields.”

Dowling (1951) proposed starting the ventral count here.

Why people look at it: It gives a definite starting point that can be found by quick inspection and is not open to interpretation, so counts made by different people agree better.

Other names: first true ventral

Source: A PROPOSED STANDARD SYSTEM OF COUNTING VENTRALS IN SNAKES (By HERNDON G. DOWLING, University of Michigan Museum of Zoology, Ann Arbor, Michigan; British Journal of Herpetology Vol. 1, No. 5, November, 1951)

“Therefore, it is recommended that the starting point for the ventral count be defined as the first plate bordered on both sides by the first row of dorsals.”

“(1) there is a definite and distinct point for beginning the ventral count which may be determined by rapid inspection and which is not subject to interpretation”

The ventral count starts after them.

Other names: preventral scales

Our main source for this term is an encyclopedia entry; it matches Dowling's rule for the first ventral.

Sources: Preventral scales (Wikipedia); A PROPOSED STANDARD SYSTEM OF COUNTING VENTRALS IN SNAKES (By HERNDON G. DOWLING, University of Michigan Museum of Zoology, Ann Arbor, Michigan; British Journal of Herpetology Vol. 1, No. 5, November, 1951)

“Preventral scales are snake scales positioned anterior to the ventral scales and are wider than they are long, but do not come into contact with the paraventral row of dorsal scales on either side of the body.”

The wide belly plates are not dorsal scales.

Why people look at it: The Navy manual says the number of dorsal scale rows is sometimes important in snake identification.

Other names: dorsals, costal scales (not the same as a turtle's costal scutes)

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Dorsals: The rows of small scales that cover the top (dorsal) surface of a snake's body. They are counted in a diagonal (or zigzag) line from the edge of the ventral plate, across the back to the opposite edge (fig. 7).”

“The number of dorsal scale rows is sometimes important in snake identification.”

“The number of scale rows all the way around the body, not counting the ventral scales.”

Count diagonally across the back, from the belly plate on one side to the belly plate on the other, leaving out the belly plates. The midbody count matters most.

Why people look at it: Smith (1943) notes that most colubrids (the family Colubridae) have 15, 17 or 19 rows at midbody.

Other names: scale rows

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.); THE FAUNA OF BRITISH INDIA, CEYLON AND BURMA, INCLUDING THE WHOLE OF THE INDO-CHINESE SUB-REGION. REPTILIA and AMPHIBIA. VOL. III.—SERPENTES. (BY MALCOLM A. SMITH; Originally published, 1943 (scan is the 1981 Indian reprint))

“They are counted in a diagonal (or zigzag) line from the edge of the ventral plate, across the back to the opposite edge (fig. 7).”

“The number of scale rows all the way around the body, not counting the ventral scales. Count the scale rows at the middle of the snake's body”

“The majority of the Colubridae have 15, 17 or 19 rows at mid-body”

“The number of scale-rows at mid-body is of much greater importance than at any other part of the body”

One number alone is the midbody count. Sources separate the numbers with hyphens, colons or spaces.

Other names: scale formula

Smith (1943) says the neck and rear counts should not be tied rigidly to a set distance from the head or vent.

Sources: Dorsal scales (Wikipedia); A new cryptic species of green pit viper of the genus Trimeresurus Lacépède, 1804 (Serpentes, Viperidae) from northeast India (Rathee YS, Purkayastha J, Lalremsanga HT, Dalal S, Biakzuala L, Muansanga L, et al. (2022) PLoS ONE 17(5): e0268402); THE FAUNA OF BRITISH INDIA, CEYLON AND BURMA, INCLUDING THE WHOLE OF THE INDO-CHINESE SUB-REGION. REPTILIA and AMPHIBIA. VOL. III.—SERPENTES. (BY MALCOLM A. SMITH; Originally published, 1943 (scan is the 1981 Indian reprint))

“When counting dorsal scales, numbers are often given for three points along the body, for example 19:21:17. These numbers correspond to the number of dorsal scales around the body at a head's length behind the head, at midbody and at a head's length before the vent. If only one number is given, it is for the midbody count.”

“21 dorsal scales one head length behind the head; 19 dorsal scales at midbody; 17 dorsal scales one head length anterior to the vent”

“When counts are made at the neck or hinder part of the body they should not be rigidly confined to any particular distance behind the head or in front of the vent”

Smith (1943) says rows are lost by absorption of the vertebral rows or of rows on the sides, usually the 3rd or 5th.

Smith doubts that the way rows are lost has much value beyond describing a species.

Source: THE FAUNA OF BRITISH INDIA, CEYLON AND BURMA, INCLUDING THE WHOLE OF THE INDO-CHINESE SUB-REGION. REPTILIA and AMPHIBIA. VOL. III.—SERPENTES. (BY MALCOLM A. SMITH; Originally published, 1943 (scan is the 1981 Indian reprint))

“The maximum number of scale-rows in the majority of snakes is at mid-body, and in most there is a reduction as the vent is approached Considerable attention has been paid in recent years to the manner in which this reduction occurs It may take place by absorption of the vertebral rows or of those on the sides of the body, usually the 3rd or 5th”

“that it has any higher systematic value is doubtful”

Row counts start here. These scales are usually slightly larger than the rows above them, and in snakes with mostly keeled scales they are usually smooth or only weakly keeled.

Other names: first row of dorsals, paraventrals

Sources: Paraventral scales (Wikipedia); A PROPOSED STANDARD SYSTEM OF COUNTING VENTRALS IN SNAKES (By HERNDON G. DOWLING, University of Michigan Museum of Zoology, Ann Arbor, Michigan; British Journal of Herpetology Vol. 1, No. 5, November, 1951)

“In snakes, the paraventral scales are the longitudinal rows of dorsal scales that contact the ventral scales. These are the first rows of dorsal scales on either side of the body and are usually slightly larger than the scales located more dorsally. In species that have mostly keeled scales, the paraventrals are usually smooth or only weakly keeled.”

“the first row of dorsals (by definition) borders the ends of the ventral plates from the anal plate anteriorly to near the head.”

Why people look at it: The Navy manual says it is often worth noting whether the dorsal scales are keeled or smooth.

Other names: keeled

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“It is often desirable to note if the dorsal scales have a longitudinal raised ridge, keeled, or if they lack such ridges, smooth (see fig. 8).”

“Keeled dorsals have a ridge down the center of each scale while smooth dorsals lack any ridge.”

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“It is often desirable to note if the dorsal scales have a longitudinal raised ridge, keeled, or if they lack such ridges, smooth (see fig. 8).”

Smith (1943) notes that keels are usually stronger in males than in females, and often stronger toward the rear of the body.

Other names: feebly keeled

Species accounts use the phrase, for example "weakly keeled middorsally", without a fixed definition.

Sources: THE FAUNA OF BRITISH INDIA, CEYLON AND BURMA, INCLUDING THE WHOLE OF THE INDO-CHINESE SUB-REGION. REPTILIA and AMPHIBIA. VOL. III.—SERPENTES. (BY MALCOLM A. SMITH; Originally published, 1943 (scan is the 1981 Indian reprint)); Central Ratsnake (Pantherophis alleghaniensis) (Virginia Herpetological Society)

“The scales may be smooth or feebly or strongly keeled , the keels are usually stronger in the males than in the females , in both sexes they are often stronger in the posterior part of the body than in the anterior”

“dorsal scales smooth laterally and weakly keeled middorsally”

They can be very hard to see.

Sources differ on the number: the Navy manual says usually paired; Whitman's key says zero to four, with the same number on every scale of one snake.

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Apical pits: Tiny depressions, usually paired, near the terminal end of each dorsal scale when present; function unknown.”

“Apical pits are small indented dots on the posterior end of each dorsal scale. They are usually impossible to see without a microscope and even then they are quite a challenge to locate. There can be zero to four apical pits, but there will be the same number on each scale of any given snake.”

In some snakes it is enlarged.

Why people look at it: An enlarged vertebral row is a character of some genera, for example Bungarus. Whitman's key warns that it can be tricky to judge.

Other names: vertebral scales

Sources: Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.); THE FAUNA OF BRITISH INDIA, CEYLON AND BURMA, INCLUDING THE WHOLE OF THE INDO-CHINESE SUB-REGION. REPTILIA and AMPHIBIA. VOL. III.—SERPENTES. (BY MALCOLM A. SMITH; Originally published, 1943 (scan is the 1981 Indian reprint))

“Vertebral Row Enlarged – The middle dorsal scale row is distinctly larger than the other rows. This character can be particularly tricky”

“In some genera, e g , Boiga, Ahætulla, and Bungarus, the vertebral series are enlarged”

In most snakes they span the full width of the belly.

Why people look at it: Smith (1943) says the number of ventral and subcaudal shields is of considerable value for telling species apart.

Other names: ventral plates, ventral scales, gastrosteges

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); THE FAUNA OF BRITISH INDIA, CEYLON AND BURMA, INCLUDING THE WHOLE OF THE INDO-CHINESE SUB-REGION. REPTILIA and AMPHIBIA. VOL. III.—SERPENTES. (BY MALCOLM A. SMITH; Originally published, 1943 (scan is the 1981 Indian reprint))

“Ventrals: The enlarged scales (scutes or plates) that extend down the undersurface of the body (fig. 9).”

“In the vast majority of snakes, large transverse scutes extend the full width of the belly.”

“The number of ventral and subcaudal shields is of considerable specific value”

“The ventral shields or gastrosteges are the enlarged scales along the mid-line of the belly They are usually transversely enlarged, much broader than long, and occupy the whole or nearly the whole width of the belly”

Why people look at it: Dowling proposed this start point so the count would begin at a point that is not open to interpretation.

Other names: ventral scale count

Source: A PROPOSED STANDARD SYSTEM OF COUNTING VENTRALS IN SNAKES (By HERNDON G. DOWLING, University of Michigan Museum of Zoology, Ann Arbor, Michigan; British Journal of Herpetology Vol. 1, No. 5, November, 1951)

“The posterior end of the ventral count is easily defined; ventrals are usually counted to, but not including, the anal plate.”

“Therefore, it is recommended that the starting point for the ventral count be defined as the first plate bordered on both sides by the first row of dorsals.”

It marks where the body ends and the tail begins. It may be entire (single) or divided by a slanting seam; some are only partly divided.

Why people look at it: Single or divided is a standard thing to record, but it can vary within one species (the Virginia account of the Central Ratsnake records both), and it does not tell you whether a snake is venomous.

Other names: cloacal plate, anal scale, anal shield, cloacal scale

Some sources prefer "cloacal plate", because the plate covers a cloaca (the shared rear opening), not an anus.

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Snake scale (Wikipedia); Central Ratsnake (Pantherophis alleghaniensis) (Virginia Herpetological Society)

“Anal plate: The large scute covering the vent. It marks the division between body and tail. It may be entire, or divided by an oblique suture (fig. 10).”

“anal plate undivided (10.8%) or divided or partially divided (89.2%, n = 232)”

“This scale has also been the anal scale, which is a misnomer since it does not cover an anus but a cloaca.”

“Fangs and venom glands are the only anatomic features that set poisonous snakes apart from nonpoisonous ones.”

The anal plate covers it, and the tail begins here.

Why people look at it: It is the landmark for snout-vent length (from the tip of the snout to the far end of the anal plate), and the point where the ventrals stop and the subcaudals begin.

Other names: cloaca, cloacal opening

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); SNAKE PARTS (Snakes in Western Massachusetts; © Tom Tyning 2013)

“Vent: The common posterior opening of the urinary, gastrointestinal, and reproductive systems of reptiles; marks the beginning of the tail in snakes.”

“The tail begins at the cloaca (the opening for both digestive product removal and reproduction) where the body ends. The cloacal opening is covered by a distinct ventral scale, called the anal plate”

“Herpetologists measure snakes from the tip of the snout to the tip of the tail for a “total length” and from the tip of the snout to the far end of the anal plate (the “snout-vent” length).”

They may run across the whole underside (single) or go only halfway, where they meet a partner (paired, also called divided). In most snakes they are paired.

Why people look at it: A count of the subcaudals is routine. Counts are often lower in females, which have shorter tails. When the subcaudals are paired, count each pair once.

Other names: subcaudal scales, urosteges, caudals

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); THE FAUNA OF BRITISH INDIA, CEYLON AND BURMA, INCLUDING THE WHOLE OF THE INDO-CHINESE SUB-REGION. REPTILIA and AMPHIBIA. VOL. III.—SERPENTES. (BY MALCOLM A. SMITH; Originally published, 1943 (scan is the 1981 Indian reprint)); Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.)

“Subcaudals: The scales or scutes under the tail; they may extend across the entire ventral surface (single), or go only half way across, where they are met by another scale (paired) (fig. 10).”

“The subcaudal scutes are usually in a double row (paired); however, in some species, all or most may be in a single row (see figure 10). A count of the subcaudals is routine.”

“Owing to the shorter tail, the number of caudals is often less in the female than in the male”

“Do not count both sides of divided subcaudals.”

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Supra-anal tubercles: Small raised keel-like structures on the dorsal scales above the vent in some snakes.”

In most snakes it simply tapers to a tip; in some it forms a spine, a bony spur or a rattle.

Our only source for this general statement is an encyclopedia entry.

Source: Snake scale (Wikipedia)

“The end of the tail may simply taper into a tip (as in the case of most snakes), it may form a spine (as in Acanthophis), end in a bony spur (as in Lachesis), a rattle (as in Crotalus), or a rudder as seen in many sea snakes.”

A newborn has a single segment, called a button, and a new segment is added at the base each time the snake sheds.

Why people look at it: The Navy manual says rattlesnakes can almost always be identified by the jointed rattle at the tip of the tail, but it is too small to rely on in pygmy rattlesnakes and in the young of some small rattlesnakes, and most of the rattle can break off, though the base usually remains. Because segments break, the number of segments does not tell a snake's age.

Other names: rattle segments

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); Timber Rattlesnake (Tennessee Wildlife Resources Agency); Prairie Rattlesnakes (National Park Service)

“Rattlesnakes are distinctively American serpents that can be almost always identified by the jointed rattle at the tip of the tail. […] It is too small to be a good field identification characteristic in the pigmy rattlesnakes (Sistrurus miliarius) and in young of some other small rattlesnakes. Although most of the rattle can easily be pulled or broken off, the base or matrix usually remains.”

“The rattle, which is used to warn predators, is tan or gray in color and consists of hollow, interlocking segments made of keratin. Newborn rattlesnakes have a single segment on their rattle, called a “button.” Each time the snake sheds, a new segment is added to the base of the rattle.”

“because rattle chambers can break, the number of rattles on a snake's tail do not indicate its age.”

In hard-shelled sea turtles it is bone covered by horny (keratin) plates called scutes; in the leatherback, blubber and skin cover it instead.

Why people look at it: Wyneken lists the carapace scutes (with the bridge scutes) as the main shell features used to identify sea turtles.

Other names: top shell, upper shell

Source: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470)

“The carapace is composed of bone covered by keratinous scutes (cheloniids, Fig. 94) or blubber and skin in Dermochelys (Fig. 95).”

“The primary scutes (Fig. 4) used as key characteristics are the marginals, laterals (costal), vertebrals, and nuchal, as well as the inframarginal or bridge scutes.”

Scutes grow at their edges and can also thicken. The seams between scutes do not line up with the joins between the bones beneath.

Other names: shell scute

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia)

“The scutes are keratinous epidermal structures that grow above the carapace bones. Scutes grow two ways. They increase in size (area) at their margins. The entire scute can increase in thickness.”

“The margins of cheloniid scutes and the bones' sutures do not align with one another (Fig. 96).”

Whether it is there at all varies, even within one species.

Why people look at it: In sea turtles, whether it touches the first costal helps tell a loggerhead (it touches) from a hawksbill (it does not).

Other names: nuchal scute, precentral

"Nuchal" is also the name of the bone beneath this scute.

Sources: Turtle shell (Wikipedia); The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470)

“At the anterior of the shell there may be a cervical scute (sometimes incorrectly called a nuchal scute); however, the presence or absence of this scute is highly variable, even within species.”

“The nuchal scute (the marginal just dorsal to the neck) is in contact with the first lateral scute.”

“The nuchal scute does not touch the first lateral scute in hawksbills. This distinguishes the hawksbill carapace from the loggerhead pattern.”

“Names of epidermal scutes in turtle shells Boulenger 1889 [31] Carr 1952 [32] Zangerl 1969 [33] Pritchard 1979 [34] nuchal precentral cervical nuchal vertebral central vertebral central costal lateral pleural costal marginal marginal marginal marginal supracaudal postcentral 12th marginal supracaudal”

The usual number is five.

Why people look at it: Their number helps separate some species: olive ridley sea turtles typically have 6 or more.

Other names: vertebrals, centrals

Sources: Turtle Carapace Anomalies: The Roles of Genetic Diversity and Environment (Velo-Antón G, Becker CG, Cordero-Rivera A (2011) PLoS ONE 6(4): e18714. Published: April 12, 2011); The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470)

“The normal number of carapace scutes in turtles is five vertebrals, four pairs of costals, and 12 pairs of marginals.”

“Olive ridleys turtles are dark grey. They typically have more than 6 normally aligned lateral scutes, 6 or more normally aligned vertebral scutes”

The usual number is four on each side.

Why people look at it: The number on each side is a sea-turtle key character: 4 in green turtles, usually 5 in loggerheads.

Other names: pleurals, laterals

Not the same as a snake's "costal" scales. "Pleural" is also the name of the rib bones beneath.

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle Carapace Anomalies: The Roles of Genetic Diversity and Environment (Velo-Antón G, Becker CG, Cordero-Rivera A (2011) PLoS ONE 6(4): e18714. Published: April 12, 2011)

“The lateral scutes are also known as costals or pleurals.”

“The carapace is smooth with 4 pairs of lateral scutes.”

“The loggerhead, Caretta caretta (Figs. 14-17), has a large head and brown carapace with 5, or sometimes 4, lateral scutes.”

“The normal number of carapace scutes in turtles is five vertebrals, four pairs of costals, and 12 pairs of marginals.”

The last pair, over the tail, are the supracaudals. The Virginia account of the Southeastern Mud Turtle gives 11 on each side.

Other names: marginals

Sources: Turtle Carapace Anomalies: The Roles of Genetic Diversity and Environment (Velo-Antón G, Becker CG, Cordero-Rivera A (2011) PLoS ONE 6(4): e18714. Published: April 12, 2011); The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Southeastern Mud Turtle (Kinosternon subrubrum subrubrum) (Virginia Herpetological Society)

“The normal number of carapace scutes in turtles is five vertebrals, four pairs of costals, and 12 pairs of marginals.”

“The last marginal scutes on each side are termed supracaudals or postcentrals (Fig. 4).”

“marginals 11/11, a single small cervical, pleurals 4/4, and vertebrals 5”

Other names: postcentrals, 12th marginals

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia)

“The last marginal scutes on each side are termed supracaudals or postcentrals (Fig. 4).”

“Names of epidermal scutes in turtle shells Boulenger 1889 [31] Carr 1952 [32] Zangerl 1969 [33] Pritchard 1979 [34] nuchal precentral cervical nuchal vertebral central vertebral central costal lateral pleural costal marginal marginal marginal marginal supracaudal postcentral 12th marginal supracaudal”

Some species have one, some two, some three.

Why people look at it: Keels can change with age: young loggerheads have sharp keels that fade as they grow.

Sources: Turtle shell (Wikipedia); The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470)

“A keel, a ridge that runs from front to the back of the animal, is present in some species. These may be single, paired, or even three rows.”

“Immature loggerheads often have sharp keels on their vertebral scutes and posterior marginal. These recede with larger size and age”

Why people look at it: Counting the rings is a convenient way to estimate the age of young turtles, but it is not as useful for older turtles, and ring counts are often unreliable for captives and for populations without a seasonal stop in growth.

Other names: growth rings, scute rings

Source: Testing the reliability of ring counts for age determination in the Egyptian tortoise (Testudo kleinmanni) (Omar Attum, Bassim Rabea, Kate Duffy & Sherif M. Baha El Din; HERPETOLOGICAL JOURNAL 21: 209–211, 2011)

“Ring counts are often unreliable in determining the age of captive animals or members of a population that do not experience the seasonal cessation of growth […]. Counting the lines or rings deposited on the shell scutes is a convenient, non-destructive method of age estimation in young individuals […], although rings are not as useful for determining the age of older chelonians”

On the plastron, the scutes meet along a central seam down the middle.

Why people look at it: The relative lengths of the segments of the plastron's midline seam can help identify a species.

Other names: scute seam

Our source for these sentences is an encyclopedia entry without a citation for them.

Source: Turtle shell (Wikipedia)

“The plastral scutes join along a central seam down the middle of the plastron. The relative lengths of the seam segments can be used to help identify a species of turtle.”

Why people look at it: In the Virginia key, a soft, pliable shell without large scutes identifies the Eastern Spiny Softshell.

Sources: Trionychidae | INFORMATION | Animal Diversity Web (By Keith Pecor); Turtle ID Guide (Virginia Herpetological Society; Last update: 10/12/2020)

“The carapace of these turtles lacks scutes and is covered instead with a leathery skin.”

“Shell soft and pliable, without large scutes; snout elongated with nostrils at tip … Eastern Spiny Softshell (Apalone spinifer spinifer)”

Over its ribs and backbone lies blubber, covered by skin with small bony plates embedded in it.

Why people look at it: In keys, a shell without scutes separates the leatherback from all other sea turtles.

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle ID Guide (Virginia Herpetological Society; Last update: 10/12/2020)

“In the leatherback, the blubber overlies ribs and vertebrae and itself is covered dorsally with waxy skin and embedded dermal ossicles (Fig. 95).”

“Shell without scutes… Leatherback Sea Turtle (Dermochelys coriacea)”

Its scutes meet in pairs along a midline seam.

Why people look at it: In sea turtles the plastron scutes are used more as landmarks for internal anatomy than for identification. In the Virginia key, the plastron's shape, hinges and number of scutes separate several freshwater turtles.

Other names: bottom shell, lower shell

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia); Turtle ID Guide (Virginia Herpetological Society; Last update: 10/12/2020)

“The bottom shell is the plastron. It also has distinct scute patterns, but these are used more often as landmarks for internal structures than for species identification (Fig. 5).”

“It comprises an upper part, the carapace, and lower part, the plastron, connected by a bony bridge.”

“8 A – Plastron with 11 scutes; posterior border of pectoral scute located anterior to the anterior margin of the bridge … B – Plastron with 12 scutes; posterior margin of pectoral scute located posterior to anterior margin of bridge, usually in contact with marginal scutes”

Some turtles also have a single intergular scute in front of them. The Virginia account of the Southeastern Mud Turtle describes a single triangular gular.

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia); Southeastern Mud Turtle (Kinosternon subrubrum subrubrum) (Virginia Herpetological Society)

“From anterior to posterior, the intergular scute is closest to the neck, then (in order) are the gular, humeral, pectoral, abdominal, femoral and the anal scutes.”

“There are six laterally symmetric pairs of scutes on the plastron: gular, humeral, pectoral, abdominal, femoral, and anal (going from the head to the tail down the seam)”

“11 plastral scutes, including a single triangular gular scute”

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia)

“From anterior to posterior, the intergular scute is closest to the neck, then (in order) are the gular, humeral, pectoral, abdominal, femoral and the anal scutes.”

“There are six laterally symmetric pairs of scutes on the plastron: gular, humeral, pectoral, abdominal, femoral, and anal (going from the head to the tail down the seam)”

Why people look at it: Its shape is used in the Virginia key: a triangular pectoral leads to the mud turtles, a squarish one to the musk turtles.

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia); Turtle ID Guide (Virginia Herpetological Society; Last update: 10/12/2020)

“From anterior to posterior, the intergular scute is closest to the neck, then (in order) are the gular, humeral, pectoral, abdominal, femoral and the anal scutes.”

“There are six laterally symmetric pairs of scutes on the plastron: gular, humeral, pectoral, abdominal, femoral, and anal (going from the head to the tail down the seam)”

“9 A – Triangular pectoral scute on plastron; no visible skin between scutes”

“B – Squarish pectoral scute on plastron; some whitish skin visible between plastral scutes”

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia)

“From anterior to posterior, the intergular scute is closest to the neck, then (in order) are the gular, humeral, pectoral, abdominal, femoral and the anal scutes.”

“There are six laterally symmetric pairs of scutes on the plastron: gular, humeral, pectoral, abdominal, femoral, and anal (going from the head to the tail down the seam)”

Not the same as a lizard's femoral pores.

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia)

“From anterior to posterior, the intergular scute is closest to the neck, then (in order) are the gular, humeral, pectoral, abdominal, femoral and the anal scutes.”

“There are six laterally symmetric pairs of scutes on the plastron: gular, humeral, pectoral, abdominal, femoral, and anal (going from the head to the tail down the seam)”

Not the same as a snake's anal plate.

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia)

“From anterior to posterior, the intergular scute is closest to the neck, then (in order) are the gular, humeral, pectoral, abdominal, femoral and the anal scutes.”

“There are six laterally symmetric pairs of scutes on the plastron: gular, humeral, pectoral, abdominal, femoral, and anal (going from the head to the tail down the seam)”

Hard-shelled sea turtles have one, and so do some other groups; many turtles do not. It is not drawn on our plastron.

Sources disagree about which groups have it.

Sources: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Turtle shell (Wikipedia)

“From anterior to posterior, the intergular scute is closest to the neck”

“A particular variation is that the Pleurodiran turtles have an intergular scute between the gulars at the front, giving them a total of 13 plastral scutes, compared to the 12 in all Cryptodiran turtles.”

Source: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470)

“Some individuals have a single unpaired interanal scute that is found between or posterior to the anal scutes.”

In hard-shelled sea turtles it carries a row of inframarginal scutes.

Why people look at it: Bridge scutes are among the key characters used to identify sea turtles.

Sources: Turtle shell (Wikipedia); The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470)

“It comprises an upper part, the carapace, and lower part, the plastron, connected by a bony bridge.”

“The primary scutes (Fig. 4) used as key characteristics are the marginals, laterals (costal), vertebrals, and nuchal, as well as the inframarginal or bridge scutes.”

“The scutes between the plastron and the carapace are the inframarginals (Fig. 5).”

The freshwater turtle in our plastron drawing has none.

Why people look at it: The usual count is a sea-turtle key character: 4 on each side in green turtles, often 3 in loggerheads, though the number varies.

Other names: inframarginals, bridge scutes

Source: The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470)

“The scutes between the plastron and the carapace are the inframarginals (Fig. 5). While the number of inframarginals is somewhat variable, the most common count is often listed as a key characteristic.”

“There are 4 inframarginal scutes on each side”

“Loggerheads often have 3 inframarginals however, this characteristic is variable.”

In the Southeastern Mud Turtle they are the only scutes on the bridge.

Other names: axillary scute, inguinal scute

Our sources name these scutes but do not describe in words exactly where they sit; the drawing puts the axillary at the front of the bridge and the inguinal at the rear.

Sources: Southeastern Mud Turtle (Kinosternon subrubrum subrubrum) (Virginia Herpetological Society); The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470)

“bridge consists only of axillary and inguinal scutes”

“two Rathke’s pores, one each in the axillary and inguinal scales”

Why people look at it: Keys use it: in the Virginia key, a hinged, movable plastron that lets the turtle close up in its shell points to the Woodland Box Turtle, and the Virginia account of the Southeastern Mud Turtle describes two plastral hinges.

Other names: hinge, hinged plastron

Sources: Southeastern Mud Turtle (Kinosternon subrubrum subrubrum) (Virginia Herpetological Society); Turtle ID Guide (Virginia Herpetological Society; Last update: 10/12/2020)

“2 plastral hinges allow considerable movement of anterior and posterior lobes”

“plastron hinged and moveable, allowing complete enclosure of the turtle in shell …… Woodland Box Turtle (Terrapene carolina carolina)”

In chameleons and most geckos they take the place of ordinary overlapping scales.

Other names: granules

Sources describe where granules occur rather than defining them.

Source: THE FAUNA OF BRITISH INDIA, INCLUDING CEYLON AND BURMA. REPTILIA and AMPHIBIA. VOL. II.—SAURIA. (MALCOLM A. SMITH, M.R.C.S., L.R.C.P. (London); Originally published 1935 (scan is the December 1974 First Indian Reprint Edition))

“The scales usually have a free posterior border and more or less overlap one another, but in the Chameleons and in most Geckoes the true scale-like structure is replaced by tubercles or granules”

In some groups only males have them; in others both sexes do.

Other names: femoral pore

Smith (1935) warns that pore counts vary between individuals and that their value for telling species apart has been much overestimated.

Source: THE FAUNA OF BRITISH INDIA, INCLUDING CEYLON AND BURMA. REPTILIA and AMPHIBIA. VOL. II.—SAURIA. (MALCOLM A. SMITH, M.R.C.S., L.R.C.P. (London); Originally published 1935 (scan is the December 1974 First Indian Reprint Edition))

“They may be restricted to the males, as in the Gekkonidæ, or both sexes may have them, as in the Lacertidæ”

“The femoral pores are arranged in a single row along the under surface of the thigh”

“The number of pores is subject to individual variation, and their value for specific determination has been much over-estimated”

Our only source describes how the pores are arranged rather than defining them.

Source: THE FAUNA OF BRITISH INDIA, INCLUDING CEYLON AND BURMA. REPTILIA and AMPHIBIA. VOL. II.—SAURIA. (MALCOLM A. SMITH, M.R.C.S., L.R.C.P. (London); Originally published 1935 (scan is the December 1974 First Indian Reprint Edition))

“the preanal pores may form an angle, the apex forwards, or be arranged in a cluster”

In geckos with toe pads, the pads arose by expansion and modification of these plates.

Why people look at it: Smith (1935) says the many pad designs are excellent characters for dividing geckos into genera.

Other names: lamellae

Source: THE FAUNA OF BRITISH INDIA, INCLUDING CEYLON AND BURMA. REPTILIA and AMPHIBIA. VOL. II.—SAURIA. (MALCOLM A. SMITH, M.R.C.S., L.R.C.P. (London); Originally published 1935 (scan is the December 1974 First Indian Reprint Edition))

“It has arisen from the cylindrical form of digit, such as the Ground Geckoes have, by expansion and modification of the plates or lamellæ upon its under surface The many designs which have been evolved in this process form excellent taxonomic characters for generic division”

Smith (1935) says they are present in all the scales of two lizard families, the Anguidae and the Scincidae.

Other names: bony plates

Source: THE FAUNA OF BRITISH INDIA, INCLUDING CEYLON AND BURMA. REPTILIA and AMPHIBIA. VOL. II.—SAURIA. (MALCOLM A. SMITH, M.R.C.S., L.R.C.P. (London); Originally published 1935 (scan is the December 1974 First Indian Reprint Edition))

“Ossifications of the cutis in the form of small bony plates, the osteoderms, are present in all the scales of the Anguidæ and Scincidæ”

In snakes the scales are not separate pieces, which is why a snake sheds its outer skin in one piece.

Other names: scales

Our source for this is an encyclopedia entry.

Source: Snake scale (Wikipedia)

“Snake scales are formed by the differentiation of the snake's underlying skin or epidermis.”

“Snake scales are not discrete but extensions of the epidermis hence they are not shed separately”

Sources use the word differently: the Navy manual uses it for any horny scale, overlapping or not; turtle sources for the horny plates of the shell; and crocodilian sources for bony plates in the skin.

Other names: scutum

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470); Crocodylia | INFORMATION | Animal Diversity Web (Author: Danny Goodisman; Last updated 9 September 2002)

“Scutes: Overlapping or juxtaposed scales that cover the surface of the body. Formed of horny skin in reptiles, differing from the bony scales of fishes.”

“The scutes are keratinous epidermal structures that grow above the carapace bones.”

“Their skin is covered with non-overlapping scales composed of the protein keratin and often studded with bony plates called scutes.”

Other names: head shield

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Shield: An enlarged scale or scute, commonly specialized and with a distinctive name.”

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Plate: A large flat scale, usually on the head or ventral surface.”

This is the usual state of a snake's back and belly scales.

Other names: overlapping

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Imbricate: Overlapping, as the tiles on a roof; the usual condition for dorsal and ventral scales. (Compare juxtaposed.)”

This is the usual state of a snake's head shields.

Other names: non-overlapping

Source: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY)

“Juxtaposed: With edges adjacent but not overlapping; the usual condition for head shields. (Compare imbricate.)”

Other names: keels

Sources: Snakes of Central and Western Africa (Hsu, ER, Davis, J, Chippaux, JP, and Jackson, K. 2017.); Turtle shell (Wikipedia)

“Keeled dorsals have a ridge down the center of each scale while smooth dorsals lack any ridge.”

“A keel, a ridge that runs from front to the back of the animal, is present in some species.”

Turtle sources use the word for the joins between shell bones.

Sources: Poisonous Snakes OF THE WORLD / A MANUAL FOR USE BY U.S. AMPHIBIOUS FORCES / NAVMED P-5099 (DEPARTMENT OF THE NAVY / BUREAU OF MEDICINE AND SURGERY); The Anatomy of Sea Turtles (Jeanette Wyneken, Ph.D.; Illustrated by Dawn Witherington; December 2001; NOAA Technical Memorandum NMFS-SEFSC-470)

“Suture: A line of division between two scales.”

“The margins of cheloniid scutes and the bones' sutures do not align with one another”

Snakes shed it in one piece. In most lizards it comes off in flakes, and crocodilians shed their scales one by one.

Why people look at it: A shed snake skin keeps the scale pattern, so a reasonably complete and intact shed can usually be identified.

Other names: shedding, sloughing

Sources: Snake scale (Wikipedia); THE FAUNA OF BRITISH INDIA, INCLUDING CEYLON AND BURMA. REPTILIA and AMPHIBIA. VOL. II.—SAURIA. (MALCOLM A. SMITH, M.R.C.S., L.R.C.P. (London); Originally published 1935 (scan is the December 1974 First Indian Reprint Edition)); Crocodylia | INFORMATION | Animal Diversity Web (Author: Danny Goodisman; Last updated 9 September 2002)

“The shedding of scales is called ecdysis, or, in normal usage moulting or sloughing. In the case of snakes, the complete outer layer of skin is shed in one layer.”

“The scales are shed individually, so crocodilians do not molt (shed their skin all at once) like snakes do.”

“The discarded skin gives a perfect imprint of the scale pattern and it is usually possible to identify the snake if this discard is reasonably complete and intact.”

“comes off in flakes”

Snakes have no eyelids: the spectacle forms before hatching, when the upper and lower eyelids fuse. It turns cloudy before a shed and comes off with the old skin.

Other names: brille, eyecap, ocular scale

Our sources for this term are encyclopedia entries.

Sources: Ocular scales (Wikipedia); Brille (Wikipedia)

“Occasionally, the term ocular scale is used without a prefix, in which case it specifically refers to the brille, also known as the spectacle [4] or eyecap. [5] This is a transparent scale that covers and protects the eye. It is formed in embryonic snakes when the transparent upper and lower eyelids fuse. Once hatched, a snake does not possess eyelids and the brille carries out some of these functions. [5]”

“In snakes, there are no eyelids and the brille is clear and cannot be distinguished, except when the animal is becoming ready for ecdysis. At that time, it becomes cloudy and is visible as a cover over the eye. When the snake moults, the brille is also shed, generally inside out, as part of its skin.”