NOMENCLATURE. 27 



depressus. Depressed ; havings a simple tooth ex- 

 tending the hinge towards the anterior part. 



excisus. Cleft ; gaping with a transverse slit. 



longitiidinalis. Longitudinal ; running nearly the 

 ivhole length of the shell. 



lateralis. Lateral ; projecting on either side. 



feflexus. Reflex ; hent or folded over the exte- 

 rior margin. 



ierminalis. Terminal j placed at the extremity of 

 the shell. 



iriincaius. Truncate ; having the beaks trans- 

 versely cut oflf, 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 impres- 

 sion. 



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. 



