358 CORBULID.E. 



The siphons are extended in Sphenia much more than in 

 Corbula, hut the foot is byssiferous, and the anal valve con- 

 spicuous; the hinge is also like that of Corbula, but the 

 habit of burrowing in oyster-shells and limestone, and the 

 general appearance of the shell, show certain affinities with 

 Saxicava. The genus should perhaps be limited to 8. 

 Binghami and Bitppellii ; the other species, described as 

 Sphenia by one of the Authors, appear to belong to the 

 genus Cryptomya of Conrad, in which the siphons of the 

 animal are short, and the shell thin and somewhat gaping 

 posteriorly. 



Species of Sphenia. 

 Binghami, Turton. Ruppellii, A. Adams. 



Genus CRYPTOMYA, Conrad. 



Shell inequilateral, transversely oblong, gaping poste- 

 riorly, surface of valves usually radiately striated, or de- 

 cussated. Hinge formed by a single, elevated, lamellar 

 tooth in the right valve, with a corresponding cavity in the 

 left valve; cartilage internal. Pallial impression with a 

 slight posterior sinus. 



Ex. C. Philippinarum, A. Adams, pi. 95, fig. 5. Shell, 

 C. Philippinarum, fig. 5, a, 5, b. 



In this genus the siphons are short, and not covered with 

 a coriaceous epidermis, and the shell is thin and decussately 

 striated. The hinge resembles that of Sphenia, but in 

 their habits the animals seem to show an analogy to those 

 of Mya and Corbula, living buried at the surface of sand 

 and mud. 



