Of the 246 specimens examined, 233 (94.7%) have the third and fourth supralabials entering each eye ([Table 3]). All snakes that have the fourth and fifth labials entering the orbit on either side also have seven supralabials on the same side. One specimen having only the fourth labial entering the eye on the right side also has six supralabials on that side, but the third supralabial is split diagonally and the part contacting the eye does not contact the lip and hence is not a supralabial. The remaining three atypical conditions (4/3 + 4; 3 + 4/3 + 4 + 5; 3 + 4 + 5/3 + 4) occur only one time each and on snakes having 6-6 supralabials.
Contact of mental with chin-shields
Of the 246 specimens examined, 190 (77.2%) have the mental in contact with both anterior chin-shields. The mental is in contact with only the left anterior chin-shield in 15 specimens, only the right anterior chin-shield in 2
specimens, and the mental does not contact either anterior chin-shield in 39 specimens. Separation of the mental and an anterior chin-shield always results from the posterior elongation of a first infralabial.
Table 3. Variation in Number of Supralabials Entering the Eye in 246 Specimens of Tantilla gracilis.
| Supralabials | Number of specimens | Per cent of occurrence | |
|---|---|---|---|
| Left | Right | ||
| 3 + 4 | 3 + 4 | 233 | 94.7 |
| 4 + 5 | 3 + 4 | 4 | 1.6 |
| 4 | 3 + 4 | 1 | 0.4 |
| 3 + 4 | 4 + 5 | 5 | 2.0 |
| 3 + 4 | 4 | 1 | 0.4 |
| 3 + 4 | 3 + 4 + 5 | 1 | 0.4 |
| 3 + 4 + 5 | 3 + 4 | 1 | 0.4 |
Dorsal scale rows
Of the 245 specimens examined for this characteristic, 228 (92.7%) have scale counts of 15-15-15-15-15. The number of scale rows around the neck and one head length behind the head are 15 except in a single specimen that has 14 scale rows at these three places. The number of scale rows around midbody is 15 in 244 of 246 specimens (99.2%); two specimens have 14 scale rows around midbody. The number of preanal scale rows is more variable; counts of 14 through 17 were recorded. Fourteen specimens have 14 preanal scale rows (5.7%), 229 have 15 preanal rows (93.1%), two have 16 preanal rows (0.8%), and one has 17 preanal rows (0.4%). Known causes for atypical numbers of preanal scale rows are listed in [Table 4]. A preanal count at one head length anterior to the anus would have omitted most of the above variation in numbers of preanal scale rows.
Table 4. Atypical Numbers of Preanal Scale Rows in Specimens of Tantilla gracilis.
| Preanal scales | Number of specimens | Cause | Per cent of occurrence |
|---|---|---|---|
| 14 | 10 | Scale rows seven and eight on left fuse within the last five ventrals | 4.1 |
| 14 | 1 | Scale row two on the right is lost adjacent to the penultimate ventral | 0.4 |
| 16 | 1 | Scale row eight on the left divides adjacent to the last ventral | 0.4 |
| 16 | 1 | A scale row is added on the right adjacent to and anterior to the anal plate | 0.4 |
| 17 | 1 | A scale row is added on each side adjacent to and anterior to the anal plate | 0.4 |