284 



POPULAR CONCHOLOGY. 



Lyrodesma. Conrad. — Shell equivalve, inequilateral, 

 hinge with about eight diverging cardinal teeth; the 

 upper surface obliquely striated. Fossil. 



Family 18. — TRIG ONI A CEA. 



The animal has the mantle divided for three-fourths of 

 its circumference, and fringed at the edges ; behind, there 

 are two simple openings and no siphons ; the foot is large, 

 strong, hatchet- shaped, bent backwards, serrated at the 

 edges, and at the side for one-third part laciniated; the 

 gills are free, large, almost triangular, with double lamellae ; 

 the mouth feelers are very small, and in part of their 

 length joined together. The shell is equivalve, inequi- 

 lateral, varying from triangular to nearly circular; the 

 inside iridescent ; in the right valve two large compressed, 

 diverging, furrowed teeth, which lock into four in the 

 other valve, the latter being only furrowed on the inner 

 side; two simple muscular, and one simple pallia! im- 

 pression. — Marine. 



Lyrodon. Sow. (Trigonia Brug.) — Shell and Ani- 



Lyrodon pectenata. 



mal described in the account of the family. — 1 species ; 

 and many fossil. 



