I204 CASTAI.INA 



the rounded posterior ridg^e ; epidermis lironze-color : teeth 

 subcompressed ; nacre light \\ine-color. 



Length 25, height 20, diam. 11 mm. 



Imbabura. Ecuador. 

 Castalia crosseana Hiuau'.o. Jl. de Conch.. XIII, 1865, pp. 316 



and 429, pi. XIV, fig. 2. 

 Tetraplodon crosseanns Simpson, Syn., 1900. p. 865. 



This species is more nearly rhomboid in form than any of the 

 Tetraplodons. The figure, which is not very finely finished, 

 represents the epidermis as a sort of olive-color, rayed with 

 burnt brown. 



Genus CASTALINA von Ihering, 1891. 



Castalina von Ihering, Zool. Anzeiger, 1891, p. 478. 



Shell somewhat triangular, inflated, but having the sides a 

 little flattened, solid, with a strong posterior ridge, the sub- 

 truncate posterior slope rising almost to a wing above; beaks 

 full, high, with nearly strictly radial sculpture; surface slightly, 

 irregularly, concentrically sulcate, sometimes a little corrugated ; 

 posterior slope generally plicate or corrugated ; epidermis thick, 

 rayless, blackish ; hinge plate arched, wide ; two to several 

 radial pseudocardinals in each valve ; two vertically or oblique- 

 ly striate laterals in the left valve and one in the right ; beak 

 cavities deep ; anterior muscle scars deep, united ; nacre whit- 

 ish. 



Animal, probably very much like that of Tctraplodon, but 

 with the mantle closed or open at the branchial and anal 

 openings. 



Type, Castalina luartcnsi von Ihering. 



The species, which are placed in this group, are evidently 

 closely allied to the genus Tctraplodon, but have, on the whole, 

 more unionoid characters. The shells are generally more com- 

 pressed, the radial sculpture is more feeble, the teeth are not 

 so strongly verticallv striate. In Castalina the pseudocardinals 

 are radial, while in Tctraplodon they are not. In the latter 

 group the mantle is closed behind into siphons while in Casta- 

 lina it may be open or closed. 



