Prymnomiodon chalceus, Cope, 1860

Lee, Justin L., Chandramouli, S. R. & Bauer, Aaron M., 2023, Tropidonotus nicobarensis Sclater, 1891 is a junior synonym of Thamnophis saurita (Linnaeus, 1766) (Squamata: Serpentes: Natricinae), Zootaxa 5285 (1), pp. 133-148 : 137-139

Redescription of Prymnomiodon chalceus

A subjective junior synonym of Thamnophis saurita sackenii fide Cope (1892). The holotype (ANSP 5286) of Prymnomiodon chalceus is an adult male specimen in good condition ( Figure 2 ), with a large ventrolateral incision on the posterior portion of the body and another incision below the vent. The tail is damaged and broken off. SVL 300 mm, TailL 38 mm (TotalL 338 mm), HeadL 14.0 mm, HeadW 7.2 mm, SnoutL 4.6 mm, EyeD 3.0 mm; TailL/ TotalL 0.112, HeadL/ W 1.95, EyeD/HeadL 0.22, EyeD/SnoutL 0.65. Head large and distinct from neck, longer than wide and wider than deep; eyes large with round pupils, smaller than half the length of the head and shorter than snout; nostrils round and oriented laterally. Rostral barely visible from above; internasals paired and wider than long, small, trapezoidal; prefrontals paired and wider than long, pentagonal, suture dividing the two scales less than half the length of the frontal; muzzle length/frontal length ratio 0.610; frontal large, longer than wide, pentagonal and shield shaped; anterior suture of frontal straight but posterior suture angled, border with supraoculars slightly convex; parietals paired and longer than wide, subhexagonal; length of each parietal longer than frontal. Loreal scale 1/1, moderately sized, slightly longer than wide and bottommost border longest; preoculars 1/1 and vertically elongate; postoculars 3/3, lowest postocular smallest in size; supralabials 8/7, with the 4 th and 5 th scales in contact with the orbit on the left side, and the 3 rd and 4 th scales in contact on the right side; 5 th or 6 th supralabial largest and rectangular shaped; temporal scale formula 1+2/1+2 on either side, with the anterior scale broad and subrectangular; infralabials 9/10, with first 1–4 scales in contact with the anterior chin shields on the left side, 1–5 scales in contact on the right side, and the 4 th scale being the largest. Dorsal scales strongly keeled, in 19–19–17 rows, ventrals 152; cloacal plate undivided; subcaudals paired, 24 on the incomplete tail.

After more than 160 years of preservation, the dorsum is bluish gray with a pale vertebral stripe around 1.5–2.0 dorsal scales wide and edged with black, extending from the posterior parietal suture to the end of the tail; on each side a barely visible lateral stripe around 0.5 dorsal scales wide is present on the 3 rd and 4 th scale row, starting at the nape near the border of the last supralabial and ending at the terminus of the remaining tail; small black edges present across each stripe. Dorsal portion of head and nape blue green; snout and supralabial region pale beige; preocular with a distinct white spot bordered anteriorly by black; lower postocular also white, but without distinct dark edges; laterally, along the lower temporals, a small black streak extends posteriorly from the eye to the nape. Ventral surface beige, immaculate, much lighter than the dorsum, lighter than dorsal stripes.

The original description by Cope (1860) indicates the specimen was originally more olive dorsally with the scales exhibiting a “metallic luster”, but overall the holotype is identical in general appearance and scale counts. Rossman (1961) also reported identical color characteristics, although he noted the bottommost postoculars had a more distinct bright spot that was not visible during our re-examination. Cope neglected to record the number of maxillary teeth but stated that the teeth were larger anteriorly and decreased in size posteriorly. We counted 31 maxillary teeth, and instead found that the teeth gradually increase in size posteriorly, resembling the typical dentition of Thamnophis saurita .

Figures

FIGURE 2. Holotype of Tropidonotus nicobarensis (ZSI 8895), dorsal (a), ventral (b), and lateral (c) views. Scale bars equal 10 millimeters. Photographs courtesy of the Zoological Survey of India.