GASTEROPODA. 



from it ; the aperture is contracted, and the upper angle of 

 each lip bears a more or less distinct tooth. 



Distribution, 2 species, Great Oolite and Coral Rag, France 

 and Germany. 



Sub -family — Bellerophontin^:. 



Genera : — Porcellla (p. 344), Bellerophon (p. 344) (with 

 Bucania), and 



Tremajtotus, Hall, 1863. 



Type, Bucania Chicagoensis, M'Chesney. 



Shell thick, aperture dilated ; having the form of Bucania, 

 but with a row of isolated oval siphonal openings along the 

 middle of the dorsal side. 



Fossil, 2 species. Upper Silurian, North America. 



? Carln-aropsis, Hall. 



Shell having a patelloid aspect. Spire usually attenuated ; 

 body whorl expanded abruptly; cavity shallow, presenting a 

 kind of septum as in Crepidula. 



Fossil, 2 species. Silurian, America. 



Family XI. — Fissurellid^e. 

 Deslongchampsia, M'Coy, 1850. 



Dedicated to Dr. Eudes Deslongchamps, the renowned French 

 palaeontologist. 



Type, D. Eugenei, M'Coy, Mor. and Lye. 



Shell patelliform, apex acute excentric ; with a wide longitu- 

 dinal anterior sulcus, produced into a rounded lobe. 



"This genus differs from Metoptoma in its ornamented surface, 

 and the front margin being produced downwards into a 

 rounded lobe. This latter structure would prevent the firm 

 adhesion of the shell." — (M'Coy.) 



Fossil, 3 species. Lower Oolites. England, Normandy, 

 Galicia. 



Family XIIL— Patellllve. 

 Helcion (Montfort, p. 278), Jeffreys. 



Etymology, a breast- collar. 



Synonyms, Nacella, Schumacher ; Patina, Leach ; Calyptra 

 (pars), Klein. 



Example, H. pellucidum. (Patella pellucida, Linne). 



Shell semioval, not resembling a peaked hat as in Patella; 



39 



