Like Xylophis captaini, the 2 other species currently recognised as valid in the genus Xylophis are restricted to the Western Ghats region of peninsular India.
Dorsal, ventral and lateral views of the head of a dead specimen of Xylophis captaini (image: Harry Taylor, Natural History Museum).
Xylophis perroteti (Duméril, Bibron and Duméril, 1854) is much larger and has only 13 (instead of 15) dorsal scale rows at midbody.
Xylophis stenorhynchus (Günther, 1875) is superficially more similar to X. captaini, but is larger (growing to over 20cm total length) and has more ventral and subcaudal scales, differently proportioned head scales, and occurs at higher altitudes. However, X. stenorhynchus is even less well known than X. captaini, and more work is required.
Dorsal, ventral and lateral views of the head of a dead specimen of Xylophis stenorhynchus (images: Harry Taylor, Natural History Museum).
A fourth species, X. indicus Beddome, 1878 is currently a subjective junior synonym of X. stenorhynchus. It is possibly valid - being even longer, more slender and perhaps lacking a collar - but the very few putative specimens are too poorly preserved to be certain at this stage. The relationships of Xylophis to other colubrid snakes is not known.