534 



MOLLUSCA 



PHYLÜM V 



Platychilina Koken {Fossariopsis Laube). Spire depressed, straight ; last wliorl 

 large, surface rough, tuberciilose. Inner lip even, witli simple margin. Trias. P. 

 pustulosus (Münst.). 



Delphinulopsis Laube. Like the last, but spire composed of loosely connected 

 whorls. Sutures deep. Body wborl witli nodose longitudinal keels. Inner lip even, 

 with Sharp margin. Trias. D. hinodosa (Münst.). 



Neritopsis Grat. (Figs. 901, 902). Spire depressed, body wliorl very large. 

 Surface witli spiral and transverse ribs or nodes, often cancellated. Inner lip 

 tliickened, witli broad, angular emargination in the middle. Trias to Kecent. 



Family 14, Neritidae Lamarck. 



Shell semi-glohose, without umhilicus or nacreous layer. Spire very short, somewhat 

 lateral; whorls rapidly hroadening, the last very large, and earlier ones resorbed 

 internally. Aperture semicircular ; margin of the ßattened or calloused inner lip often 

 with teeth. Operculum calcareous, with a lateral spiral nucleus, and a process for 

 muscle attachment on the inner side. Trias to Recent. 



The Neritidae are partly marine, and partly fresh-water inhabitants. The former 

 live usually in the vicinity of the coast, the latter often in brackish water. Since the 

 earlier whorls are internally resorbed, moulds of the interior reveal no trace of the spire. 

 This character, together with the form of the operculum, serves to distinguish the 

 family from the Naticopsidae, from wliich both it and the terrestrial Helicinidae 

 are probably descended. Fossil forms not infrequently retain traces of tlieir former 

 coloration. 



Neritaria- Koken {Protonerita Kittl). Spire acuminate, suture deej), surface 

 smootli. Outer lip sharp ; inner lip callous, flattened. Resorption of the inner walls 

 incomplete. Trias. 



Nerita Linn. (Fig. 903). Thick, ovoid or semi-globose, imperforate. Surface 

 smooth or with spiral ribs. Inner lip callous, flattened, with a straight, often 

 denticulate border. Operculum sub-spiral. Trias (?) to Recent. 



(?) Oncochilus Pethö (Fig. 904). Smooth ; inner lip arched, callous, bearing two or 

 three teeth on the margin or smooth ; outer lip sharp. Trias and Jura. 



Lissochilus Pethö (Fig. 905) ; Neritodomus Morr. and Lyc. ; Neritoma Morris. 

 Jura. Otostoma d'Arch. ; Dejanira Stol. Cretaceous. 



Velates Montf. (Fig. 906). Depressed conical, only the curved apex of the spire 

 Abc 



Fig. 903. 



A, Nerita laffoni Merian. Citharella Limestone ; Bpfen- 

 hofen, near Schaffliavisen, Switzerland. B, N. granulosa 

 Desh. Eocene (Sables Moyens); Auvers, near Paris. C, 

 Operculum of a recent Nerita. 



Oncochilus chromaticus Zittel. Upper 

 Tithonian ; Stramberg, Moravia. 



visible. Last whorl very large. Inner lip convex or straight, with denticulate margin. 

 Abundant in the European Eocene ; sometimes attaining a size of 10 or 12 cm. 



Neritina Lam. (Fig. 907). Sniall, semi-globose, lustrous, smooth or spiny, mostly 

 brilliantly coloured. Inner lip flattened, with sharp or fiiiely toothed margin ; outer 

 lip Sharp. Inhabits brackish or fresh water. Abundant in Tertiary and Recent. The 

 supposed Mesozoic forms belong principally to Nerita. 



