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 |
The complete dorsal scale formula for KU 83620, a male, is as follows:
[Textual representation of dorsal scale formula.]
Specimen 83620 is the only one for which we have determined the complete dorsal scale formula. Obviously the formula is complex, and possibly the specimen is atypical in this regard. Nevertheless, addition and reduction of scale rows is apparent on other specimens and can be easily observed by examining specimens under a dissection microscope.