EXPLANATION OF PLATE 7. 



Fig. 1. Arctostrea atkinsi Raymond. Right valve, viewed from the interior, 

 distal end below. The bases of several barnacles may be seen. Slightly over 

 three-fourths natural size. 



Fig. 2. The same specimen, viewed from the posterior (concave) side, to 

 show the great thickness of the shell. The distal end is below. Eight-tenths 

 natural size. 



