_SUB-ORDER B PLATYPODA 461 
Platyceras, Conrad (Acroculia, Phil.), (Fig. 887). Apex bent and spirally inrolled. 
Surface smooth, striated, plicated, or covered with small spines. Cambrian to Trias. 
The fusion of this genus with Capulus, as proposed by some authors, is hardly 
justifiable. 
Platyostoma, Conrad (Strophostylus, Hall), (Fig. 888). Shell composed of numerous 
rapidly widening whorls. Spire low, body whorl very large. Inner lip reflected and 
somewhat thickened. Aperture round, of large size. Silurian to Carboniferous. 

Fic. 888. Fic. 889. 
Fic. 887. Platyostoma niagarensis, Horiostoma Barrandei, Mun.-Chalm, 
Platyceras neritoides, Phil. Car- Hall. Devonian; Waldron, Lower Devonian ; Gahard, Ille-et- 
boniferous ; Vise, Belgium. Indiana. Vilaine (after Munier-Chalmas). 
Horiostoma, Munier-Chalm. (Fig. 889). Shell thick, spirally ribbed, with short 
lateral spire, and wide umbilicus. Devonian. 
Tubina, Barr. Silurian. Rothpletzia, Simonelli. Tertiary. 
Hipponyx, Defr. (Cochlolepas, Klein), (Fig. 890). Shell thick, obliquely conical to 
cup-shaped. Beak straight, rarely spiral, greatly removed posteriorly. Aperture oval or 
rounded, internally with a horseshoe-shaped muscular impression. The foot 
often secretes a thick, operculiform calcareous disc. Cretaceous to Recent. 
Galerus, Gray (Calyptraea, p.p. Lam.). 
Shell thin, conical, with central spiral 

Fic. 890. Fic. 891. 
Hinypo SRE apenas 5 te Yeon tn . Fia. 892. 
ipponyx cornucopiae, Lam. Cal- Crepidula ungui- 
eaire Grossier; lLiancourt, near formis, Lam. Plio- Calyptraea trochiformis, Lam. Caleaire Grossier ; 
Paris. A, Shell. 2B, Foot-plate. cene ; Tuscany. Damery, near Epernay. 
apex. Whorls flattened, often spinose. Base horizontal; aperture wide, depressed. 
Cretaceous to Recent. 
Crepidula, Lam. (Fig. 891). Slipper-shaped, elongate-oval, flat or arched. Beak 
at the posterior end, almost marginal, somewhat curved. Aperture greatly elongated, 
wide ; inner lip formed by a thin horizontal lamella. Cretaceous to Recent. 
Crucibulum, Schum. ; Calyptraea, Lam. (Fig. 892). Tertiary and Recent. 
Family 5. Naticidae. Forbes. 
Shell with short spire and large body whorl. Aperture semi-circular to oval, angular 
posteriorly, broadly rownded anteriorly. Operculum calcareous or horny, paucispiral. 
Marine. Trias to Recent. 
The distinction of fossil Naticidae trom Naticopsis, Nerita, and Ampullaria is 
