[There is no abstract or summary for this work; the following is offered in HTML format, it is the first description of many within this article. Editor March 2009] Dentalium thetidis, sp. nov. Shell white, rather thin, tapering and very little curved. Sculpture: seven elevated ribs run the whole length of the shell, those on the concave side are stronger and wider apart than the others; each interspace is grooved by a dozen fine even striae, faintly crossed by growth lines; towards the aperture one or two interstitial riblets arise. Anal orifice simple. Length, 8 mm.; diameter of aperture, 1 mm.