Gonyosoma is a genus of colubrid snakes.
There are a few distinct morphological characteristics that distinguish Gonyosoma from Elaphe. In scutellation there are 2-3 supralabials that contact the eye, with typically two in G. oxycephalum, and three in G. jansenii. The supralabial at the posterior eye is highly arched around the back of the eye. The loreal scale is thin and elongate, and appears stretched between the preocular and the nasal. Other diagnostic features include an elongate left rudimentary lung (70-141 mm), and a distinct hemipenes structure.
These snakes have the ability to laterally compress and inflate the first 3rd of their bodies when threatened. The inflated region is typically recoiled into an S, which is elevated above the horizontal forming a typical striking position. The inflation of the body exposes the black and white diagonal bands of the interstitial skin, which is particularly distinct in G. oxycephalum (Schulz 1996). In combination these adaptations impose a most ominous threat!