The snake Taeniophallus nebularis, new species, is known from a single specimen collected in montane cloud forest, 800 m above sea level, Península de Paria, northeastern Venezuela. It is a small “xenodontine” colubrid (adult male, 492 mm total length); dorsal scales in 19-19-17 rows, smooth, with paired apical pits anteriorly; brown dorsally and grayish laterally, with ill-defined pattern; white postocular stripe; and bright yellow midventrally between serrated black edges.

The species is easily diagnosed, although assignment to Taeniophallus is problematic. However, a few suggestive characters are shared with T. brevirostris and T. nicagus. These species, presumably the closest geographic relatives of T. nebularis, occur in the Amazon basin and the Guianas, indicative of a biogeographic parallel with certain plants. Taeniophallus occipitalis, with extreme scale-row reduction and a distinctive color pattern possibly derived from a brevirostris-like precursor, is widely distributed south of the Amazon. Four additional species of Taeniophallus s.l. comprise the monophyletic affinis species group centered in southeastern Brazil.

The genus Echinanthera (also centered in southeastern Brazil) is sometimes expanded to include all of Taeniophallus. Echinanthera s.s. is viewed as a demonstrably monophyletic group of six named species, whereas relationships of the subgroups of Taeniophallus s.l. among themselves and to Echinanthera remain uncertain.

Evolutionary divergence in copulatory organs of the otherwise similar Taeniophallus nicagus and T. brevirostris is extraordinary, suggesting that uncritical weight cannot safely be assigned to hemipenial characters of presumptive relatives. The hemipenis of Taeniophallus nebularis differs from those of other taxa discussed in being conspicuously bilobed for nearly a third of its length. However, some degree of bilobation is symplesiomorphic for these snakes, as evidenced by presence or absence of weak bilobation in a few species and divided insertions of retractor muscles in all. The penial asulcate interspinal gap in T. nebularis also might be symplesiomorphic for Taeniophallus s.l. and Echinanthera s.s., but homologies and level of generality for this character are not yet clear.