60 GENERA OF SHELLS. 



conic, concave beneath, vertex perforated ; 

 spire none ; foramen ovate or oblong. 



F. picta, nimbosa, crassa, Grœca, nodosa, Cayenensis, lila- 

 cina, rosea, Barbadensis, radiata, viridula, hiantula, pustula, 

 fascicularis, Javanicensis, depressa, Peruviana, gibberula, 

 minuta, alternata. 



PiLEOPsis. Shell obliquely conic, curved 

 forwards, apex hooked, subspiral ; aperture 

 round-elliptic ; anterior margin shortest, acute, 

 subsinuate ; posterior broader and rounded, an 

 elongated, arched, transverse muscular impres- 

 sion under the posterior margin. 



P. Ungarica, mitrula, intorta, subrufa, spirirostris, retor- 

 tella, pennata, squamaeformis. 



CALYPTRiEA. Shell conoid, orbicular at base ; 

 vertex erect, imperforate, pointed ; base round, 

 cavity with a convolute lip, or a spiral dia- 

 phragm. 



C. extjnetorium, laevigata, equestris, tectum-sinense, — 

 striata. 



Crepidula. Shell ovate or oblong, gener- 

 ally convex on the back, concave beneath ; 

 spire strongly inclined to the margin ; aper- 

 ture partly closed by a horizontal lamina. 



C- fornicata, porcellana, aculeata, unguifonnis, dilatata, 

 Peruviana, — depressa, glauca, plana, intorta, convexa. 



Ancylus. Shell thin, obliquely conic ; apex 

 acute, curved backwards ; aperture oval ; mar- 

 gins very simple. 



A. lacustris, fluviatilis, spina rosae, — rivularis. 



