MARSHALL (1988) described the genus Ponderimlla and it was placed in the family Vitrinellidae Bush, 1897, after comparison of the conchological characters of Ponderimlla lignkola with the vitrinellid species of the genera Anulkallus Pilsbry & McGinty (1946), Eurelema Pilsbry & Olsson (1952), Tomura Pilsbry & McGinty (1946) and Vitrinella C.B. Adams, 1850. No comparison of the radula and operculum was made. HASEGAWA (1997) described Ponderinella major, keeping it in Vitrinellidae, but the author mentioned that the operculum is paucispiral, which is not the case in any known vitrinellid species. On the contrary, this type of operculum exists in Tornus subcarinatus (see FRETTER & GRAHAM, 1978), which is the type species of the genus Tornus, after PONDER (1994). Because the species included in Ponderinella are very similar in radula and operculum to those of Tornus and they do not present important anatomical differences, we consider Ponderinella belonging to Tornidae instead of Vitrinellidae.

Shell minute, depressed-turbiniform, thin, glassy, smooth, umbilicate. Protoconch of about 1,3 convex whorls. Teleoconch whorls convex, base and umbilical rim angulate. Animal externally rather typical of the family (male unknown). Radula taenioglossate. Central tooth cutting area broadly 'V'-shaped, serrated, 2 basal denticles, ventral process U-shaped. Lateral tooth cutting area at inner third, broadly angulate and serrated. Inner marginal cutting area very broad, comb-like. Outer marginal cutting area short.
Remarks. Among described vitrinellid genera, Ponderinella lignicola bears a superficial resemblance to the type-species of Annulicallus Pilsbry and McGinty (1945), Eulerema Pilsbry and Olsson (1952), Tomura Pilsbry and McGinty (1946), and Vitrinella C. B. Adams, 1850 in general facies. They all have lower spires, however, and with the exception of Teinostoma (Annulicallus) lituspalmarum Pilsbry and McGinty, 1945, they lack a basal angulation. Teinostoma (A) lituspalmarum has a much thicker inner lip and a callus-filled umbilicus. Despite the lack of detailed comparative anatomical data on these genera, it seems extremely unlikely that these tropical and subtropical, shallow water West American species are closely related to the present deep-sea, wood-associated species. Ponderinella lignicola is the only vitrinellid known to live on wood, although additional material is needed to ascertain whether or not the association is fortuitous.

Shell minute, depressed-turbiniform, thin, glassy, smooth, umbilicate. Protoconch of about 1,3 convex whorls. Teleoconch whorls convex, base and umbilical rim angulate. Operculum paucispiral. Radula: Central tooth with the cutting edge broadly "V" shaped, serrated, 2 basal denticles, ventral process U-shaped. Lateral tooth cutting area at inner third, broadly angulated and serrated. Inner marginal cutting area very broad, comblike. Outer marginal cutting area short.