The supralabials are either six (usually) or seven on a side (Table 1).
When seven supralabials are present on either one or both sides, the
addition results from one of the following conditions: a) 5 is divided
to form 5 and 6 (N = 6); b) 2 and 3 form 2, 3, and 4 (N = 1); c) 5 and 6
form 5, 6, and 7 (N = 12); d) 4, 5, and 6 form 4, 5, 6, and 7 (N = 1);
e) 1 and 2 form 1, 2, and 3 (N = 1); f) 1, 2, and 3 form 1, 2, 3, and 4
(N = 1); g) 2 is fused with the nasal, and 3 and 4 are reduced to
granules (N = 1); h) type of addition unknown (N = 5).
TABLE 1. Variation in Number of Supralabials (N = 245) and
Infralabials (N = 246) of Tantilla gracilis.
------------+----------+-----------+------------+---------+----------
Number |Number |Per cent |Number |Number |Per cent
of |of |of |of |of |of
Supralabials|specimens |occurrence |infralabials|specimens|occurrence
------------+----------+-----------+------------+---------+----------
6-6 | 221 | 90.2 | 5-5 | 5 | 2.0
6-7 | 10 | 4.1 | 5-6 | 4 | 1.6
7-6 | 10 | 4.1 | 6-5 | 5 | 2.0
7-7 | 4 | 1.6 | 6-6 | 229 | 93.1
| | | 6-7 | 1 | 0.4
| | | 7-6 | 2 | 0.8
------------+----------+-----------+------------+---------+----------
In three of the four specimens with 7-7 supralabials, the type of
addition is the same on each side, whereas the other specimen has a
different type of addition on each side. Of the 23 examples for which
the type of addition is known, 19 (82.6%) have the increase in number on
the posterior half of the series.
In one specimen the third supralabial on the right is diagonally divided
and the resulting upper part does not contact the edge of the lip; hence
the specimen has 6-6 supralabials.