205 MYA. 



marked with faint lines. The sinus is small, and the 

 right valve is provided with a large spoon-sha]Ded 

 hinge-tooth, on which is the ligament. Shell rather 

 thin, white, with ashy epidermis. . Length one inch 

 or more. 



Mya arenaria^ Linn., M3'-a' ar-e-na'-ri-a. Fig. 176 

 represents the inside of the left valve of this well 

 known and higly valued mollusk. The shell is 

 oblong-ovate, thin and brittle, gaping at the ends, 

 whitish, and covered near the edges with a gray epi- 

 dermis. The left valve has a large spoon-shaped 

 hinge-tooth, supporting the ligament and fitting into 

 an appropriate flattened space on the right valve. The 

 pallial sinus as shown in the cut is deep, for this 

 mollusk is an active burrower, and the muscle scars 

 are unequal. The common length of the shell is two 

 or three inches. 



Though very common on the Atlantic coast, this 

 clam was unknown in San Francisco bay before the 

 year 1874. In November of that year a few speci- 

 mens were discovered near Oakland and were named 

 Mya Hemphilli, Newc, on the supposition that it was 

 a new species. In a little time, however, its true 



