SEELET — OK EOSSIL BIVALVE SHELLS. 



47 



be 



2:F'l 



And in the lower valve under the umbo are two teeth 



and a little subordinate one (constant however), and the cartilage- 



pit; its formula will therefore be 



2 1 F 



Putting the valves to- 



gether, 



2F.1 



21F 



no other genus has a like hinge 



will be the generic character for Crassatella ; and 



Anomia 

 Ostrea . 

 Lima . . 



Thracia 



LIST OF GENERIC FORMULAE. 



Types with a single Cartilage under the Umbo : F. 



Pecten . 



' F ' ^ with four central mus- 



• F • ' cular impressions. 



• F* 



Tjf~. ; attached. 



• F • m axis anteriorly in- 



• j? • 5 clined to a straight 



hinge line.* 



Mya . . 

 Tugonia 



' J ' m axis perpendicular to 

 ' F • ' a straight hinge line. 



^ S 



1/ 



§ With an Ossicle in the Cartilage : O. 



T! o ; s. 



Anatina . ^y- ; O ; S. 



Types with Teeth in addition to the Cartilage. 



1 * F * 



Chamostrea ^^jf: » 

 Avicula . 1 . ^ . v 



A 1-1/1 



Anapa . . 



1F1- 



Ervilia. . 

 Plicatula . 



1F1- 

 •1F1- 



1:F:1 



attached. 



0 , , "1F1" umbo of attached 

 Spondylus valve reC eding 



with age. 



Grnathodon \ ^ \ : S. 



Cardi 



ima 



3F2 



1-F-l 

 1-1F1 



M 1-1F1 



esodesma— rF -~ ;Sr 



Crassatella r H^m* ; L. 



Lutraria 



Mactra 



Codakia 



Scrobicularia 



21F 



•il 2 lF 

 • 2 1 F • 



2 l • 2 1 F • 2 l 

 22F-1 

 1-2FT 



•2F1-1 



;S. 

 ; S. 



Semele. . 

 Ungulina 



1-11F1 



1-2F1 

 1-2F1 

 •2F- 

 •2F- 



S. 



* The direction of the axis might be marked by a line ; thus, Lima / ; Pecten | ; 

 Avicula \ . 



