96 CARDINAL TEETH. 



gated ; including Cardita, which has the umbones nearly 

 terminal. Pachymya may probably be included, but the 

 hinge is not known. Fig. 121, 124, and 130. 



3. Hippopodium. One elongated cardinal tooth. Fig. 129. 



4. Megalodon. Hinge broad, septiform, with a large tooth 

 in the centre of one valve. Fig. 127. 



5. Isocardia. Teeth laminar ; umbones spiral. Fig. 126. 



6. Cardilia. The same, with a septiform posterior laminar 

 tooth. 



7. Hippagus. Shaped like Isocardia, without teeth. Fig. 



128. 



CARDILIA. Desh. Fam. Cardiacea, Lam A genus formed for 

 the reception of Isocardia semi-sulcata, Lam. and a small fossil 

 shell, which Deshayes had formerly named Hemi-cyclonosta 

 Michelini; thus described, (translation) " shell oval, oblong, 

 longitudinal, white, heart-shaped, ventricose, with large promi- 

 nent umbones ; hinge with a small cardinal tooth and a pit at 

 the side; a spoon-shaped projection for the reception of the 

 internal ligament ; anterior muscular impression rounded, not 

 deep ; the posterior being upon a thin, horizontal lamina, pro- 

 jecting in the anterior." Deshayes further remarks that although 

 the animal is unknown, the relations of the genus may be 

 established by means of the shell alone. Two families contain all 

 the shells which have the internal ligament inserted in a spoon - 

 shaped projection ; in the one, that of the Anatinse, the ligament 

 is supported upon a little bone, which is not soldered to the 

 hinge ; in the other, that of the Mactraceee, this little bone has 

 no existence. In the former, all the shells are inequivalve ; in 

 the latter equivalve. And M. Deshayes, considering that the 

 valves are equal, and that there is no separate bone to the 

 hinge, is of opinion that the genus ought to be placed near the 

 Lutrarise, and not far from the Anatinse. C. semisulcata, fig. 

 501, 2. " 



CARDINAL MARGIN. The edge of a bivalve shell on which 

 the teeth is placed. 



CARDINAL TEETH. The teeth upon the hinge directly beneath 



