OTHER BIVALVE MOLLUSKS 



109^ 



beaks near the posterior end, sinus small, right valve 

 inflated, left valve flattened. The shell is beauti- 

 fully white and smooth, with line lines of growth, 

 and the interior is shining and silvery. It is a south- 

 ern species, and it grows to a length of two inches, 

 though most specimens are shorter. 



P eri plo ma discus, 

 Stearns, the Round Lan- 

 tern-shell, is well shown 

 in Figure 85. This fine 

 species was discovered at 

 Long Beach, Cal., not 

 many years ago, and for 

 a time specimens were 

 very rare. Afterwards 

 a considerable number 

 were washed up on the 

 beach, though it is by no 

 means a common shell. 

 The valves are white, ex- 

 ceedingly thin and frag- 

 ile, almost circular in 

 outline, though with one 



square corner. The diameter of a large specimen is 

 nearly two inches. 



A delicate little shell, of 

 which Figure 86 represents 

 a large specimen, found at 

 various points along the 

 coast and also in San Fran- 

 cisco Bay, is named Lyonsia calif ornica, Conr., the 

 California Lyonsia. The shell is bulged at one 



Fig. 85 (*) 



Fig. 86 



