Writing about variation in ventrals in the West Indies they state, “Trinidad is 18 to 19 kilometres from the nearest point on the mainland of Venezuela in the north and = 13 kilometres in the south (across the delta of the Orinoco River) and Tobago is 28 to 29 kilometres from the nearest point on Trinidad (near Toco). The differences in ventral counts between specimens from Trinidad and adjacent Venezuela, compared to specimens from Trinidad and Tobago, are striking. Mean ventral numbers in Trinidad are lower by approximately 8 to 15 scales than specimens from adjacent Venezuela. On Tobago, ventral numbers again increase markedly over those in Trinidad and are even higher than those from mainland Venezuela. In fact, only specimens from upper Central America have higher ventrals than those of specimens from Tobago. The mean for ventrals for Trinidad males is 20.2 scales lower than that for Tobagan males. Comparable figures for females are not available, but the count for the single Tobagan female is 9 scales above the highest count for Trinidad females. Ventral numbers decrease in the Guianas (material available only from Guyana and Surinam) as compared to adjacent areas in Venezuela, as well as in Brazil, Uruguay and Paraguay, but increase again in Argentina (the pattern in the latter 4 countries is poorly understood due to the paucity of material).”
Thus, it seems highly unlikely that Tantilla melanocephala is a single, widespread species. The ventral counts given by Wilson and Mena for Trinidad (137- 152 in males and 147-159 in females) do not even overlap with their numbers for Tobago (157-160 for males and 168 for a single female).