Shell turbinate, conical, solid with a thick lip, spire elevated; operculum multi-spiral.
TYPE SPECIES Herpetopoma scabriusculum (Angas, 1867).

The type species of Herpetopoma, Euchelus scabriusculus Adams & Angas in Angas, 1867, from southern and south-eastern Australia, is a small gemmate species with a simple, open umbilicus bordered by a strongly beaded spiral cord. The columella is likewise relatively simple with a single well-developed tooth at its base. Another well-developed tooth is situated on the basal lip, close to its junction with the columella, the space between these teeth forming a deep U-shaped notch. The inner margin of the outer lip is set with numerous small, ridge-like denticles and the operculum is openly multispiral, with a broad growing margin.
Herpetopoma has frequently been treated as a subgenus of Euchelus, but like most more recent authors, I consider it to represent a distinct radiation and to be worthy of recognition at generic level. Species of Euchelus s.s. are generally larger and have an operculum with fewer, more rapidly expanding whorls (see above). Although they may have a single simple tooth/denticle at the base of the columella, they mostly lack the characteristic pattern of two teeth at the junction of the columella and basal lips, separated by a U-shaped notch, which is typical of Herpetopoma. Species of Euchelus s.s. are generally larger shelled than those of Herpetopoma, have a single weak columella tooth and lack a deep U-shaped notch at the base of the columella. Evidently Euchelus s.s. is scarce in the south-western Indian Ocean. Other taxa (e.g. Ascetostoma, Clypeostoma and Danilia) that exhibit this last feature have additional characters, which set them apart from Herpetopoma.
However, even when recognised as a genus itself, Herpetopoma, may prove to be a composite taxon, given the diversity of shell form evident in the species assigned to it. I have reasonable confidence that H. instrictum, H. seychellarum, H. serratocinctum and H. stictum are correctly placed in this genus and refer them to Herpetopoma sensu stricto. However, I am less certain about H. helix, H. naokoae and H. xeniolum and thus consider them Herpetopoma sensu lato. The protoconch is more exsert and evidently less strongly sculptured, the juvenile microsculpture sometimes granular rather than vermiform and, at least in H. helix, the operculum is tightly multispiral throughout.
Radula: Formula oo+(3-4)+l+(3-4)+oo; ca 55 transverse rows of teeth; transition from lateral to marginal series relatively clear. Rachidian with broad, trigo¬nal cusp and well-developed hood; cusp with strong transverse ridge at its base, this generally concave due to medial indentation near cusp base; cutting edge coarsely dentate, central denticle largest, lanceolate, with 2-4 smaller denticles on each side. Lateral teeth progressively decreasing in size from first to last, but not markedly so; one specimen with 3 pairs of laterals per row, another with four; cusp elongate-trigonal to spathulate, bearing coarse lateral denticles on both margins (3-6). Marginals longer and more slender than laterals, but relatively shorter than in other genera; inner marginals distinctive in having a slender, recurved cusp with a few short, barb-like denticles near the tip on inner margin and a series of much longer, close-set, curved denticles on outer margin, the central part of the cusp appearing as a rib-like structure from which the two series of denticles project; remaining marginals with smaller, ladle-shaped cusps with a finely pectinate margin, the outermost one with a somewhat enlarged cusp.

The main features of the Herpetopoma species are ridge-like denticles inside the outer lip, a basal colurnellar tooth and another tooth on the basal lip near the columella, the two teeth making an U-shaped notch (Herbert, 2012). Considering the type species, Herbert add to this features an open umbilicus, characterizing Herpetopoma sensu striata. I use here an extending characterization for a Herpetopoma sensu lato in which Herbert locate for instance H. naokoae Poppe, Tagaro & Dekker, 2006.