48 CALIFORNIA SEA SHELLS. 



anchor, it enjoys the rush of air and water, and 

 fears no danger. This species can easily be dis- 

 tinguished from the last by its brown, glossy 

 epidermis and conspicuous ribs. The shell is 

 purple, but more or less whitish. Some old 

 specimens, with nearly obsolete ribs, grow to a 

 length of eight or ten inches. The soft parts 

 are orange colored, and are frequently eaten. 



Resembling the mussels are the Modiolas, 

 several species of which are found on the coast. 

 The shells are bulged near the hinge line, and 

 extend beyond the umbo on one side. Modiola 

 cajjax, Conr., is covered with a glossy, brown 

 epidermis, mossy in parts. The animal binds 

 itself by a strong byssns, and seems to seek se- 

 cluded places under stones, where it can be found 

 at low tide. Modiola recta, Conr., is " long, 

 thin, narrow and angular, with chafl-like hairs.'' 



Among the difficult things to explain is the 

 fact that a mollusk, with a thin, flexible shell, 

 can bore a deep hole into hard rock. That this 

 is done, however, can be proved bv any one who 

 will examine the work of the Pea-pod Shell, 

 Adula falcata, Gld., Fig. J, PL XIII. The 

 shell is long, narrow and slightly curved ; the in- 

 side is white and pearly, while the outside is cov- 

 ered with a dark chestnut epdermis, which has 

 numerous transverse wrinkles. I found the rocks 

 of Duxbury Haef, at Bolinas, almost alive with 

 this and other borers. The deep, narrow holes 

 are curved to fit the shell, and the animal also 

 spins a byssus, which it attaches to the sides of 

 its burrow ; length, two inches. Adula stylina, 



