12 



FAMILY NERITOPSID^E. 



Animal with large head, and distant, elongated tentacles, the 

 eyes on short peduncles at the exterior -base, buccal orifice plicate, 

 foot obtuse at either extremity, operculigerous disk surrounding the 

 operculum, columellar muscle forming a ring interrupted above, 

 mantle-margin thickened and papillary. Dentition, 8*l'(2-f-0-|-2)*l*8, 

 PLl,fig.l. 



Shell imperforate, neritiform, solid, columellar lip not dentate, the 

 margin with a sinus in the middle. Operculum thick, calcareous, 

 symmetrical, not spiral, with lateral, median nucleus, the exterior 

 face convex, the interior face divided into two unequal parts, the 

 columellar margin with a median appendage. 



Fossil opercula of this family, occurring frequently without the 

 shell, were long objects of doubt to scientists, and have received the 

 names of Peltarion, Deslongchamps. 1858 (PI. 1, figs. 5, 6), Sca- 

 phanidea and Cyclidea, Rolle. 1862, and Hypodema, Koninck. 1853. 

 They have been supposed to be the beak of a cephalopod, a valve 

 of a brachiopod or of a chiton, and an operculum of the polyp 

 Calceola. 



Genus NERITOPSIS, Grateloup. 1832. 



General characters those of the family. Shell white, cancellated 

 by spiral and longitudinal ridges and striae. Operculum having on 

 its exterior face and columellar margin a large truncate appendage, 

 interior face depressed, with a labral, semilunar, smooth part, and 

 a striate columellar part, with a pit on either side of it. (PI. 1, figs. 

 7, 8). Radula, Gray, 1840, is a synonym. East Indies, Polynesia. 

 N. RADULA is the only recent species. Fossil, secondary and ter- 

 tiary. 



Genus ^ATICOPSIS, M'Coy. 1844. 



Shell imperforate, naticiform, thick, suture plicate; columella 

 callous, more or less flattened, sometimes minutely tuberculated or 

 transversely plicate, lip sharp (PL 1, fig. 17). Operculum something 

 like Neritopsis, with convex exterior face, the interior face un- 

 equally two-parted, one part smooth, the other rugose, no appen- 

 dage on the columellar margin (PL 1, figs. 13, 14). 

 Devonian-Triassic. 



Europe, India. 



I included this group in Naticidse (Vol. viii, 8) ; the operculum, 

 however, shows it to be a member of the present group. Nerito- 

 mopsis, AVaagen. 1880, Carboniferous of India, is a synonym. 



