Trachischium fuscum

The blackbelly worm-eating snake, or Darjeeling slender snake, is a colubrid snake endemic to Asia. Its Latin name means dusky or dark brown, matching both belly and back, which are black or dark brown, the back sometimes with lighter lengthwise streaks. The back scales are in 13 rows, and males have keeled scales on the sides in the vent region (Wikipedia, general species account).

Adults may reach 51 cm in total length, with a tail of 6 cm. It is found in Nepal and India (Jammu and Kashmir, northern West Bengal, Uttarakhand, Sikkim, Assam, eastern Arunachal Pradesh).