| Fig. 31.—Shell of Crucibulum, seen from below so as to show the inner whorl b, concealed by the cap-like outer whorl a. |
| Fig. 32.—Animal and shell of Ovula. |
| b, Cephalic tentacles. d, Foot. h, Mantle-skirt, which is naturally carried in a reflected condition so as to cover the sides of the shell. |
Fam. 35.—Xenophoridae. Foot transversely divided into two parts. Xenophorus. Eotrochus, Silurian.
Fam. 36.—Capulidae. Shell conical, not coiled, but slightly incurved posteriorly; a tongue-shaped projection between snout and foot. Capulus. Thyca, parasitic on asterids. Platyceras, extinct.
Fam. 37.—Hipponycidae. Shell conical; foot secreting a ventral calcareous plate; animal fixed. Hipponyx. Mitrularia.
Fam. 38.—Calyptraeidae. Shell with short spire; lateral cervical lobes present; accessory genital glands. Calyptraea, British. Crepidula. Crucibulum.
Fam. 39.—Naricidae. Foot divided into two, posterior half bearing the operculum; a wide epipodial velum; shell turbinated. Narica.
Fam. 40.—Naticidae. Foot large, with aquiferous system; propodium reflected over head; eyes degenerate; burrowing habit. Natica, British. Amaura. Sigaretus.
Fam. 41.—Lamellariidae. Shell thin, more or less covered by the mantle; no operculum. Lamellaria. Velutina. Marsenina, Oncidiopsis, hermaphrodite.
Fam. 42.—Trichotropidae. Shell with short spire, carinate and pointed. Trichotropis.
Fam. 43.—Seguenziidae. Shell trochiform, with canaliculated aperture and twisted columella. Seguenzia, abyssal.