Trochid��e

Trochid��e, a family of gasteropodous molluscs of the order Pectinibranchiata. The shell is conical and spiral and more or less nacreous; the aperture is entire and closed by a thin horny operculum. In the genus Trochus the shells are top-shaped, and hence are popularly known as Top-shells. Many of the shells are extremely beautiful, and are used for adorning head-dresses, necklaces, &c., the outer layers being removed. There are a large number of British species, and a multitude of foreign and fossil forms. The Trochid��e are closely allied to the Turbinid��e.