SEELET — ON FOSSIL BIVALYE SHELLS. 
47 
' 2 • F ' 1 
be — '- . 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 r^YW^ ' I^^^^i^g valves to- 
' 2 F 1 ~ 
gether, . 2iy- ' ^^^^ ^® generic character for Crassatella ; and 
no other genus has a like hinge. 
LIST OF GEXERIC FOE^^fUL^. 
Tyjpes with a single Cartilage under the Umbo : F. 
Anomia — with four central mus- 
• F • ' cular impressions. 
_ -F- 
Ostrea . . 7-^-. ; attached. 
Lima 
Thracia 
F • axis anteriorly in- 
"j^- ' clined to a straight 
hinge line.* 
Pecten ^ . axis perpendicular to 
• F • ' a straight hinge line. 
Mya . . . 
Tugonia . .-^ ; S. 
§ With an Ossicle in the .Cartilage : O. 
r|r.;0;S. 
Anatina . ^ ; O ; S. 
Types icith Teeth in addition to the Cartilage. 
Avicula . 
1 * F * 
Chamostrea ., „ ; O. 
1 • F • 1^ 
1 • F • 1' 
A 1 • !/• 1 
Anapa . . 
•IFl- 
Ervilia. . 
Plicatula . 
IFl- 
•IFl- 
1:F:1 
attached. 
o J T 'IFl* umbo of attached 
bpondylus .yT^TY-' valve receding 
with age. 
2 • F • 1 
Gnathodon ^ . . ^ ; S. 
1-Fl 
i Cardinia • 1 • 1 F • 1 
M , 1-lFl „ 
esodesma— -;S. 
* 2 F ' 1 
Crassatella .^2Tf^- ' ^' 
Lutrana . . . ; S. 
^ 2'-2iF-2' 
Mactra . ^ tt,-, S. 
Codakia . 
2'-2iF-2' 
2-2F-1 
1'2F1- 
Scrobicularia -j^t^^ty^. ; S. 
Semele. . 
Ungulina 
1'2F1 
1'2F1 
•2F- 
•2F- 
* The direction of the axis might be marked by a line ; thus, Lima / ; Pecten | ; 
ivicula \ . 
