[1] This genus, almost entirely represented by extinct species, is of slender form and elevated, evenly and gradually acuminate spire, conspicuous development of the spiral lyrae and short aperture.

It should evidently be considered especially with Trypanotoma and allies, but it is somewhat of an annectant form, as the American species at least have true ribbing on the nepionic whorls which becomes completely lost on the larger volutions of the shell.

The embryo in the type, Pleurotoma basteroti Desm., of the European Miocene, is said by Cossmann to be paucispiral, but the drawing shows a multispiral protoconch.

The anal sinus is broad, sometimes very feeble and always median in position on the spire whorls though not identified with any particular one or more of the subequal and rather coarse flat spirals.

There can be but little doubt, in view of geographical variations and wide distribution of this genus, that Endiatoma, of Cossmann, should be regarded as a synonym or as constituting a slightly differentiated section of Asthenotoma.