98 CAEDILIA. 



are ventricose, and have regular radiating ribs. Tlie family 

 contains the genera Cardium, Cardita, Cypricardia, Hiatella, 

 Isocardia, and others enumerated in the explanation of figures 

 122 to 130. Their characters may be thus explained. 



1. Caedium. Two cardinal and two lateral teeth in each 



valve, including Hemicardium, Papyridea and Aphrodita, 

 in the last of which the teeth are nearly obsolete. Pig. 

 122, 123, 123*, 123**. 



2. Venebicaedia. Two oblique cardinal teeth, one elon- 



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. Rg. 127. 



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



6. Caedilia. The same with a septiform posterior laminar 



tooth. 



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



128. - - 



CAEDILIA. Desh. 1837. Hemictclonosta. Fam. Cardiacea, 

 Lam. A genus formed for the reception of Isocardia semi-sulcata. 

 Lam. and a small fossil shell, which Deshayes had formerly named 

 Hemicyclonosta Michelini ; thus described, (translation) " shell 

 oval, oblong, longitudinal, white, heart-shaped, ventricose, with 

 large prominent 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, 

 projecting in the anterior." Deshayes further remarks that 

 although the animal is u.nknown, the relations of the genus may 

 be established by means of the shell alone. Two families con- 

 tain all the shells which have the internal ligament inserted in 

 a spoon-shaded projection ; in the one, that of the Anatinse, the 

 ligament is siipported upon a little bone, which is not soldered 

 to the hinge ; in the other, that of the Mactracese, this little 



