Genus Cheilophis Gilmore, 1938

TYPE SPECIES. — Cheilophis huerfanoensis Gilmore, 1938.

EMENDED DIAGNOSIS. — Cheilophis can be differentiated from all other snakes by its unique combination of features: wide haemal keel (on the posterior mid- and posterior trunk vertebrae) that bears a constriction at around its mid-length and becomes wider and blunt wedged-shaped at its posterior termination; distinct “notches” of the haemal keel in ventral view; ventral expansion of the haemal keel in lateral view; thick neural spine that is mostly confined at the posterior portion of the neural arch; relatively thin zygosphene with a distinct median lamina (“lip”) and prominent lateral lobes; moderately vaulted neural arch; deep posterior median notch of the neural arch; deep interzygapophyseal constriction; almost circular cotyle and condyle; widely extended parapophyseal process of the paradiapophyses; almost horizontal to only slightly dorsally inclined prezygapophyses; and large prezygapophyseal and postzygapophyseal articular facets. In addition to these vertebral characters, Rage (1984b) also indicated the following cranial features as diagnostic for the genus: palatal process of the maxilla directed backwards; surangular lamina of the compound bone higher than the prearticular; coronoid present.