NESTLERS. 183 



Petricola carditoides^ Conr. , Pe-trik'-o-la car-di- 

 toi^-des, as its name indicates, is a dweller in the 

 rocks. Normally, the shell is oval, with regular 

 sculpturing; but it has the habit of boring into a 

 soft rock, or getting into a hole that was there before, 

 and then growing to fit the premises. From this 

 cause it happens that representatives of this species 

 vary very much in their general appearance. Some- 

 times one is long and narrow, while its neighbor is 

 shaped like a fat bean. 



The ligament is external; the hinge-teeth and the 

 sculpturing sometimes become nearly obsolete, and 

 the shell becomes thick and rough. Its color is a 

 dinory white, and it is from an inch to two inches in 

 length. It is found in rocky places, all along the 

 coast. 



Riipellaria lamellifera^ Conr., Ru-pel-la'-ri-a lam- 

 el -lif-e-ra. Fig. 156, is a near relative of the last 

 species. It is essentially a nestler 

 among the rocks, and it may be 

 known by the ten or twelve large, 

 thin, concentric frills or laminae 

 which mark its periods of growth. 

 Fig. 156. ^}^g shell is strong, somewhat angu- 



lar, white, and about an inch in length, though it 

 sometimes g-rows laro:er. I have occasionally found 

 live specimens at Monterey. 



There are three species of Saxidomi which live in 

 the sand and gravel along the seacoast, from British 

 Columbia to Mexico. They resemble one another in 

 form and habits. The beaks are placed far forward, 

 and behind them is the large external ligament. 

 The first species is named Saxidomus aratics^ Gld. , 

 a-ra^-tus. The general shape of the 



