GASTEROPODA. 



Example, P. bilobatum. iTpper Lias, Normandy. Pig. 11. 

 Calcareous plates nearly circular or transversely oval ; ante- 



rig. 11. 



rior border rounded, posterior produced and truncated ; concave 

 above and flattened below ; tbe two faces have one-half smooth 

 and the other concentrically striated in an inverse direction 

 to each other. 



Fossil, 3 or 4 species. Up. Lias — Cor. Eag. England; 

 Normandy ; Wurtemberg. 



CLASS IL— GASTEEOPODA. 

 Order I. — Prosobrajstchiata. 

 Family IL — MuRiciDiE (see p. 212, &c.). 



The genera included in this family are : — 



MuREX, Typhis, Pisania, Trophon, Fasciolaria, Turbi- 

 NELLA [Cynodonta, Latirus, Lagena), EusTJS [Glavella, Chryso- 

 domus, Pusionella, Tritonidea), EuLGUR, Comestella, Myris- 

 TICA, and Lachesis 



AiiTACHis, H. and A. Adams. 



Type, Columbella scalarina, Sowerby. 



Shell like Columbella; operculum elongated, unguiform, 

 nucleus terminal, having close analogies with Fisania. 

 Distribution, 27 species. Tropical America. 



Ptychatracttjs, Stimpson, 1865. 



Etymology, ptycJi, a fold ; atractus, a spindle. 

 Type, Easciolaria ligata, Mighels and Adams. Deep water ; 

 United States. 



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