In this glossary you will find definitions of all the characters used in the key listed in alphabetical order. In some cases, helpful usage tips are include for certain characters. In addition to the thumbnail images included in the key, you should use this glossary as a reference during each step of your identification.
Each character listed below has a numerical ranking of 1, 2, or 3 based on how reliable and easy it is to use. Try to use as many easy (1) characters as you can before moving on to medium (2) and hard (3) characters. Clicking on the name of a character will jump down to its full definition below. The illustration below is provided as a general reference. To view images specifically for an individual character, click on the image thumbnails in the key.
Though not mentioned in the below characters, there are also other characters that are present in the keys. These characters are subjective in nature and are not nearly as reliable as the below characters, but may provide some guidance in the event that no other options are available.
This illustration displays each scale used as a feature for identification in the key (for ease of use, it is not comprehensive).
Head Characters
Body Characters
# of Rows between Upper Labial and Eye
Rows between Upper Labial and Eye - The number of scale rows between the upper labial and the eye. Do not include perioculars in this count. This character is only relevant to viperids.
# of Upper Labials in Contact with Eye
Upper labials in contact with the eye - The number of upper labial scales that touch the edge of the eye. There are usually 1-3, although suboculars can sometimes separate all of them from the eye.
Apical Pits
Apical Pits - 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.
Anterior Temporals
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.
Chin shields
Chin Shields - The paired, symmetrical scales on the ventral side of the head that separate the two rows of lower labials. There are usually two pairs of chin shields, but 1 or 3 pairs can also be found in some species. If there are more than 2 scales spanning the distance from one row of chin shields to the other, then they are not chin shields. The first pair of chin shields is often separated from the symphysial by the first pair of infralabials.
Cloacal Scale
Cloacal scale - The last scale anterior to the cloaca, immediately posterior to the ventrals. It is often much larger than the ventrals and it covers the cloaca. It is either single or divided.
Dorsal Scale Rows
Dorsal Scale Rows - 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 - if you count immediately posterior to the head or anterior to the cloaca, the number may be incorrect.
Dorsal Scale Shape
Straight vs. Oblique - Straight dorsal scales are symmetrical and are more typically diamond-shaped. Oblique dorsal scales have one side that is longer than the other and are more trapezoid-shaped, making it seem as if they are angled slightly towards the ventrum of the snake. Check the dorsal scales all along the body, as some snakes are considered to have oblique scales but they are only oblique on part of the snake's body.
Dorsal Scale Texture
Dorsal Scales Smooth vs. Keeled - Keeled dorsals have a ridge down the center of each scale while smooth dorsals lack any ridge.
Head Scale Shape
Head Scale Shape - the general shape of the scales of the head. Head scales can either be large and plate-like, or small and undifferentiated.
Internasals
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.
Interoculars
Interoculars - the number of scales between the eyes on a viperid snake. Do not include the perioculars in this count.
Keeled Ventrals
Keeled Ventrals - A sharp double-keel to the ventral, giving the appearance of ridges on the margin of the snakes ventrum.
Loreal
Loreal - The scale(s) between the preocular(s) and the nasal scale. It is sometimes absent.
Lower Labials
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.
Maxillary Dentition
Fangs - Fangs are enlarged teeth that are specialized for venom delivery. They are found on the anterior end of the maxilla (the upper jaw bone) in viperids, elapids, and atractaspidids as well as on the posterior end in some colubrids. The presence or absence of fangs, as well as fang type, is used to define dentition types:
- Aglyph - lacking any enlarged tooth. Teeth should appear relatively uniform in size, with no tooth distinctly larger than the rest.
- Opisthodont - An enlarged tooth on the posterior end of the maxilla without any groove or modification. Fang should be towards posterior end of maxilla and distinctly larger than other teeth.
- Opisthoglyph - An enlarged tooth on the posterior end of the maxilla with a lateral to anterolateral groove present.
- Proteroglyph - An enlarged, tublar fang at the anterior end of the maxilla that is rigid, and short in comparison to a solenoglyph fang.
- Solenoglyph - A very large tublar fang at the anterior end of the maxilla that this mobile, folding either frontwards or sideways.
Nasal Division
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. It is single if the nostril does not contact the edge of the scale. The nostril itself can vary in size and location.
Perioculars
Perioculars - the number of scales around the eye of a viperid snake. Count every scale in contact with the eye.
Postoculars
Postoculars - The scale(s) immediately posterior to the eye. If there is more than one, the top one is considered the superior, the bottom one is the inferior, and if there is a middle one, it is considered to be the middle.
Prefrontals
Prefrontals - The scale(s) immediately posterior to the internasal(s). They are usually paired and symmetrical but sometime there is only a single scale.
Preoculars
Preoculars - The scale(s) immediately anterior to the eye. If there is more than one, the top one is considered the superior, the bottom one is the inferior, and if there is a middle one, it is considered to be the middle.
Pupil Shape
Pupil Shape - The pupil can be round, horizontally elliptical, or vertically elliptical. On a dead snake, even if the eye is slightly elliptical, it is considered elliptical.
Rostral
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. It is usually rounded and does not extend much beyond the lower jaw. However, some species have an elongate rostral that extends beyond the lower jaw and/or has a very distinctive shape. The rostral is also grooved underneath to allow the snake's tongue to be flicked in and out while the mouth is closed.
Subcaudal Division
Subcaudals divided/single - Subcaudals are sometimes found in two rows and are then considered "divided" - Do not count both sides of divided subcaudals. Undivided subcaudals are called single.
Subcaudal Number
Subcaudals - The scales on the ventrum of the snake posterior to the cloaca. They are sometimes found in two rows and are then considered "divided". Do not count both sides of divided subcaudals.
Suboculars
Suboculars - The scale(s) between the eye and the supralabials. They are not suboculars if they contact the loreal, nasal, or temporals.
Supraoculars
Supraoculars - The scale(s) directly above the eye. Typically one on each side of the head, they separate the eye from the frontal. Occasionally there are two, or zero supraocluars.
Upper labials
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.
Ventral Scale Number
Ventral Scales - The wide scales on the underbelly of the snake. They must be wider than long to count as ventrals. Only count those anterior of the cloaca.
Vertebral Scale Row Keel
Vertebral Row Double-Keeled - The middle dorsal scale row has two keels on each scale.
Vertebral Scale Row Size
Vertebral Row Enlarged - The middle dorsal scale row is distinctly larger than the other rows. This character can be particularly tricky when dealing with oblique scales--some snakes with oblique scales simply appear to have an enlarged vertebral row because the vertebral scales are not overlapped as the other dorsal scales are. If your snake is strongly oblique, you might consider not using this character in your identification.