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Podopsis. Shell inequivalve, subregular, adhering by the inferior beak, 

 not auriculated, the lower valve largest, most convex, and the beaks most 

 produced; hinge without teeth. 



2 fossil species. 



Ligament internal. 



OSTRACEA.— Five Genera. 



This family is separated into two divisions. 



DIVISION I. Ligament internal, or demi-internal. Shell irregular, 

 foliated, sometimes very thin. 



DIVISION II. Ligament demi-internal. Shell foliated, and often 

 very thick. 



Gryphea. Shell free, inequivalve, the lower valve large, concave, ter- 

 minating by a projecting, involute beak, the upper valve small, flat, and oper- 

 cular; hinge without teeth; an oblong, arched, cardinal pit; only one muscular 

 impression in each valve. 



G. angulata, 11 fossil species. 



Ostrea. Shell adhering, inequivalve, irregular; beaks distant, becoming 

 very unequal by age, and the upper valve gradually during the life of the 

 animal; hinge without teeth. Ligament demi-internal, inserted in the cardi- 

 nal pit of the valves; the pit of the lower valve increasing by age, sometimes 

 to a great length. 



0. edulis, 



0. parasitica, 



0. margaritacea, 



O. grucella, 



' hippopus, 



' denticulata, 



' gibbosa, 



' folium, 



' borealis, 



' spathulata, 



' austral is, 



1 labrella, 



' Adriatica, 



' ruscuriana, 



' elliptica, 



' plicatula, 



' cochlear, 



' Virginica, 



' haliotidea, 



' glaucina, 



' cristata, 



' Canadensis, 



' de for mis, 



' fusca, 



' gallina, 



' excavata, 



' fucorum, 



' turbinata, 



' numisma, 



' mytiloides, 



' cornucopia?, 



' cristagalli, 



' lingua, 



1 sinuata, 



' cucullata, 



' imbricata, 



' tulipa, 



' trapezina, 



' doridella, 



' hyotis, 



' Brasiliana, 



' tuberculata, 



' rubella. 



' radiata, 



' scabra, 



' rufa, 



' limacella, 



33 fossil species. 



' rostralis. 









Vulsella. 



Shell longitudinal, subequivalve, irregular. 



i free; the bez 



