PART II. ATRACHIA. AVICULID^. 385 



elevated ; umbones terminal ; the posterior end some- 

 times rostrated. (Jig, 126, «.) 



L. dactylus. 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. f. 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. ^04. f. 5. 



Pern A. Shells sometimes irregular, inequi valve, 

 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 Modiola; 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 theligament; umbones terminal..(^^.126.«.) 

 C. Mytiloides. 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 Corhula, &c. 



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

 c c 



