NOMENCLATURE. 27 



depressus. Depressed ; having a simple tooth ex- 

 tending the hinge towards the anterior part. 



excisus. Cleft ; gaping with a transverse slit. 



longitudinalis. Longitudinal ; running nearly the 

 whole length of the shell. 



lateralis. Lateral ; projecting on either side. 



reflexus. Reflex; bent or folded over the exte- 

 rior margin. 



terminalis. Terminal ; placed at the extremity of 

 the shell. 



truncatus. Truncate ; having the beaks trans- 

 versely cut off, and the hinge placed within 

 them. 



Costa cardinis. Hinge rib ; an elevated line run- 

 ning from the hinge internally to the infe- 

 rior margin. 



Cicatrix. Cicatrix; internal muscular im- 

 pression. 



Dens. Tooth; an acute projection within the 

 hinge, by which the valves are united and 

 often articulated. 



anticus. Anterior; the tooth nearest the liga- 

 ment, or on the side of the area. 



