Shell very thin, conical, tubular, involuted in a loose and irregular spiral manner; aperture circular, edges sharp, interrupted in the middle by a notch prolonged like a slit through nearly all its length, stopped abruptly at some distance from the summit. Siliquaria anguina. S. muricata. S. lævigata. S. lactea. _S. anguina._ The Snake Siliquaria. Pl. 33, fig. 4. Shell tapering, undulating, spiral at the extremity. _S. muricata._ The Prickly Siliquaria. Species armed with short spines or prickles; aperture sometimes margined; usually of a rosy or pink colour. FAMILY II. MALDANIÆ. Two genera. 1. Clymene. One species. _C. amphistoma._ The double-mouthed Clymene. Tube thin and slender, open at both ends; incrusted externally with sand and fragments of shells. 2. Dentalium. The Tooth Shell. Twelve species. This genus took its name from its resemblance to an elephant’s tooth. It is an attenuated conical tube, slightly bent, and open at both ends. Shell tubular, regular, symmetrical, lightly curved longitudinally, conic, attenuated insensibly posteriorly, and open at each extremity by a round orifice. Dentalium elephantinum. D. aprinum. D. fasciatum. D. entale. D. Tarentinum. D. corneum. D. octoganum. D. novemcostatum. D. dentale. D. nigrum. D. politum. D. eburneum. _D. elephantinum._ The Elephant’s Tooth Shell. Species in which the tube is striated or ribbed longitudinally; the ribs are generally ten in number; green colour. _D. entale._ The common Dentalium. Pl. 33, fig. 1. Species very minutely striated; white or yellowish colour. _D. pellucidum._ The pellucid Dentalium. Species narrow and thin; pale topaz colour. _D. politum._ The ring-striated Tooth Shell. Species finely pointed, solid, striated annularly; generally rosy or pink colour. _D. rectum._ The straight Tooth Shell. Species entirely straight, with longitudinal ribs. _D. eburneum._ The Ivory Tooth Shell. Species of a reddish or pale yellow colour, with the tip frequently tinged with orange or pink. FAMILY III. AMPHITRITÆA. Four genera. The similarity of the four genera comprising this family is such, that it was thought sufficient to give only one type (the sabellaria crassissima), as the student may easily recognise the others. 1. Pectinaria. Two species. A membranous or papyraceous tube, in the form of a reversed cone; unfixed; exterior covered with sandy adhesions.