OTHER BIVALVE MOLLUSKS 105 



Ensis californicus^ Dall, the California Razor- 

 shell, is a rare species, found from Monterey south- 

 ward. It is delicate, narrow, slender and curved. 

 Length, about two inches. 



The members of the Mactrida:^ which we are now 

 to consider, may be distinguished by the triangular 

 pit for the cartilage, which is situated in the midst 

 of the hinge-teeth. The shells are mostly quite thin, 

 with sharp edges, and are often partly or wholly 

 covered with a thin epidermis. 



Mactra nasuta^ Gld., the 

 Beaked Mactra, resembles 

 Figure 82, a figure which 

 shows the general appear- 

 ance of several species of 

 this group. The shell is 



^ , . . tig. i-2 



of moderate size, and is 

 scattered widely along the coast. 



Mactra calif ornica, Conr., the California Mactra, 

 has a rather small shell, somewhat depressed behind 

 the furrowed beaks, which are about midway be- 

 tween the ends of the shell. It is from an inch to 

 an inch and a half in length. 



Mactra dolabriformis, Conr., the Mattock Mac- 

 tra, occurs from San Diego southward, and so 

 scarcely comes into our list. The shell is com- 

 pressed, and is of a polished white under a dull 

 brown epidermis. In the hinge-area the ligament is 

 separated from the cartilage pit by a shelly plate. 

 This fine shell grows to a length of three and a half 

 inches. 



