ASIPHONIDA. 



481 



posterior ear. The hinge-line is furnished with numerous 

 cartilage-pits (fig. 340, B), and the anterior ear is compara- 

 tively small. The species of the genus are principally 

 Mesozoic, though a few Tertiary forms are known. Bake- 

 wellia, of the Permian, resembles Gervillia in general form, 

 but the cartilage-pits are few in number, and the hinge is 

 provided with anterior and posterior teeth. The Devonian 

 Actinodesma is probably a still older relative of Gervillia. 

 In this connection also must be placed the singular Triassic 

 genera Cassianella and Hoernesia, the former extending also 

 into the Jurassic. In Cassianella (fig. 340, D and E) the 



Fig. 340. Types of Aviculidte. A, Gervillia HartmanniLia.s ; B, Part of hinge of the 

 same, enlarged ; c, Hoernesia Joannis-Austrice, slightly enlarged Trias ; D and E, Cassianella 

 grypJieata, of different ages Trias. (After Miinster and Laube.) 



shell is thick and very inequivalve, the right valve being 

 flat or concave, while the left is strongly convex. The hinge- 

 line is straight, with a few small teeth, and there are short 

 ears. In Hoernesia, again (fig. 340, c), the left valve is simi- 

 larly inflated, with a similarly incurved beak, but cartilage- 

 pits are present, a single strong tooth exists in both valves, 

 and the hinge-line is crenulated. 



Nearly related to both Gervillia and Perna is the import- 

 VOL. I. 2 H 



