84 



WEST COAST SHELLS 



Fig. 60 



prominent. 



The shell is oval, and when fresh it is of a fine olive- 

 green color, which bleaches to cream. In each valve 

 there are three cardinal hinge-teeth, the middle one 

 beiniz cleft. The form of the shell is shown in Fig- 



Venerupis lamellifera^ Conr., the 

 Rock-Venus, is shown in Figure 60. 

 The shell is white, very irregular, and 

 is marked with many thin, concentric 

 laminae, which sometimes are ver}^ 

 There may also be a trace ot obso- 

 lete ribs. In habit it is a nestler among rocks. Very 

 young specimens are often purple tinteci. Some speci- 

 mens are considerably larger than the figure. 



Figure 61 gives two good 

 views of Psephidia lordi^ 

 Baird, Lord's Pebble-shell, a 

 plump little bivalve which 

 lives off the shore, below the 

 tide line, from Alaska to 

 southern California. In color it is white or pale 

 tinted. The figures are much enlarged. 



Fsephidea ovalis^ Dall, the Oval Pebble-shell, is 

 larger, more oval, and more compressed. The shell 

 is white and polished. Its range is about the same 

 as that of the last species. Viviparous. 



Genuna gemnia^ Totten, the Gem-shell, is a very 

 small bivalve recently introduced into San Francisco 

 bay, with seed oysters from the Atlantic. The 

 shells are nearly round and are marked with delicate, 

 concentric ridges. The color is white, or they may 

 be tinged with purple. Many specimens are not 



Fig.61.xi (*) 



