Shell more or less turreted, generally tuberculated; aperture small, oval, oblique; the columellar edge hollowed, callous; the right edge sharp, and dilating a little with age; operculum horny, oval, rounded, sub-spiral, and striated. Cerithium giganteum. C. palustre. C. sulcatum. C. telescopium. C. ebeninum. C. erythræonense. C. muricatum. C. radula. C. crassum. C. decollatum. C. nodulosum. C. vulgatum. C. obeliscus. C. granulatum. C. aluco. C. echinatum. C. subulatum. C. heteroclites. C. zonale. C. semiferrugineum. C. torulosum. C. tuberculatum. C. morus. C. obtusum. C. semigranosum. C. asperum. C. lineatum. C. vertagus. C. fasciatum. C. ocellatum. C. literatum. C. atratum. C. eburneum. C. punctatum. C. lima. C. perversum. _C. vertagus._ The curved beak Cerithium. Pl. 24, fig. 3. Species with evidently a small canal, very short, and recurved obliquely towards the back. _C. aluco._ The caterpillar Cerithium. Species with a canal much smaller, but entirely straight, and a sinus well formed at the posterior union of the two edges. _C. semigranosum._ The semi-granulated Cerithium. Fusiform, turreted; apex acute; the suture with double spiral rows of large granules; minutely striated transversely, with sulcated granulations; colour reddish brown. 2. Pleurotoma. Twenty-three species. Distinguished from the Cerithium by having a notch or slit in the right margin. Shell fusiform, rather rugged, spire turreted; aperture ovate, small, terminated by a canal variable in length; the right edge sharp, more or less notched; operculum horny.