PART II. ATRACHIA. AV1CULIDJ3. 385 



elevated ; umbones terminal ; the posterior end some- 

 times rostrated, (fig. 126. t.) 



L. daetylus. Sow. Man. f. 161. 



Mytilus Linn. Shell transverse, somewhat triangular, 

 from the straightness and elevation of the hinge mar- 

 gin ; umbones minute, terminal, sometimes with an 

 obsolete tooth. 



M. achatinus. Sow. Man. 158. 



Lanistes Humph. Shell oval, transversely cardiform, 

 ventricose ; umbones prominent, with diverging ele- 

 vated striae ; hinge margin not elevated or angulated; 

 teeth none : the cardiform type. 



discors. En. Meth. 204. f. 5. 



PERNA. Shells sometimes irregular, inequivalve, 

 oyster-shaped, greatly compressed ; the margins 

 brittle ; hinge plate broad, with numerous teeth, se- 

 parated by parallel grooves containing the ligament, 

 and gaping near the umbones. 



Gervillia Def. General form of M odiola ; hinge long, 

 straight, with small, irregular, transverse grooves. 

 Fossil only. 



G. avicularis. Sow. Man. f. 169. 



Crenatula Lam. Irregularly oval, compressed; hinge 

 margin straight, with a few semicircular excavations, 

 containing the ligament; umbones terminal. (Jig. 126. a.) 

 C. Mytilo'ides. Sow. Man. f. 168. 



Perna Lam. Shape various; valves always equally flat- 

 tened; but the hinge margin always straight, not pro- 

 longed; the plate marked with numerous transverse 

 regular grooves. 



P. Ephippium. Sow. Gen. f. 166. 



Pulvinites Def. Valves unequal, one being flat, the 

 other convex ; hinge short, grooved, as in the last : 

 representing Corbula, &c. 



P. Adansoni. Sow. Man. f. 170. 

 c c 



