A New Gartersnake (Thamnophis) from Tamaulipas

Abstract

RANGE.-Forested mountains near La Joya de Salas, Tamaulipas, from approximately 3,600 to 7,000 ft. DIAGNOSIS.-A narrow mid-dorsal stripe bounded on either side by a single row of black-edged blotches, their lower margins usually involving the lowermost body scale row or the outer edges of the ventrals; no lateral stripes; body scales in 17-17-15 rows; a low number of ventrals and subcaudals. Differs from T. phenax in having a lower body scale formula, fewer ventrals and subcaudals (Table I), and in the presence of a mid-dorsal stripe; from T. scalaris in the absence of lateral stripes, the great lateral extent of the blotches, greater number of maxillary teeth, and in details of head pattern. DESCRIPTION OF TYPE.-A young male; total length 368 mm., tail 85 mm. Head sharply distinct from neck. Body scales in 17-17-15 rows, reducing to 15 at a point above the 98th ventral on the left side, the 92nd on the right, by the loss of the third row. Ventrals 147, anal entire, subcaudals 68. Head shields normal, preoculars 1-1, postoculars 3-3, anterior temporals 1-1, posterior temporals 2-2, upper labials 7-7, third and fourth entering the rbit, lower labials 10-8. A narrow light mid-dorsal stripe about one scale wide extending from posterior part of parietal throughout length of body and basal third of tail, interrupted rather broadly by posterior half of nuchal blotch and narrowly at several points by black margins of lateral blotches. Lateral blotches in a single series on each side, numbering 44-45 on body anterior to vent, dark olivebrown in color, broadly outlined with black, laterally their margins involving outer edges of ventrals. Blotches covering from two and a half to four dorsal scale lengths, the interspaces about one scale length; on neck and anterior part of body blotches tending to alternate, posteriorly opposite. Upper surface of head mostly pale brown, parietals sparsely mottled with dark, forming no definite pattern. Posterior margins of internasals and prefrontals blackish, as are also the sutural margins of the more anterior upper labials. A narrow, irregular black postocular stripe involving portions of upper two postoculars, crossing center of anterior temporal, lower secondary temporal and sutural area between upper labials 6 and 7. Chin and anterior throat whitish, remainder of ventral surface dull bluish-gray. VARIATION.-Six paratypes agree with the holotype in having the dorsal scales in 17-17-15 rows, preoculars 1-1, and postoculars 3-3. Variations in other features of scutellation are shown elsewhere (Table II). In one paratype the anal scute is divided basally, the division not extending into the distal half. With a single exception the series is remarkably uniform in pattern. In this one the dorsal blotches fade out on the third scale row. On the anterior third of the body the blotches lack the usual dark borders ventrally; posteriorly on the body