OTHER BIVALVE MOLLUSKS 111 



white, and covered with a brown epidermis. There 

 is an oscicle, or little detached piece of shell, under 

 the hinge. The greatest diameter of the shell is 

 about one inch. This is a singular instance of a thin 

 shell deriving protection from the bodies of the ani- 

 mals by which it is concealed. 



Our next species is named Entodesma saxicola, 

 Baird, the Rock Entodesma. It is a singular crea- 

 ture, living in holes of various shapes and taking 

 whatever form seems most convenient. The shell is 

 somewhat oblong or pear-shaped, bulging at the 

 hinge end, gaping beneath, and prolonged around 

 the siphons into an irregular process consisting 

 chiefly of epidermis. Internally the shell is white, 

 while externally it is very rough and unsightly, being 

 partly covered with a brown periostracum. When 

 dry it is usually more or less bent or broken, owing 

 to the unequal shrinkage of the hard parts and the 

 covering. A large oscicle covers the hinge internally. 

 This is especially a northern species. 



The southern shell, Entodesma inflata^ Conr., the 

 Puffed Entodesma, resembles the last, but is smaller, 

 thinner, and more irregular, and is composed largely 

 of epidermis. It is narrow in front, wider and thin- 

 ner behind, and is about an inch or less in length. 



V erticordia novemcostata^ Ad. & Rve., the Nine- 

 ribbed Verticordia, has a minute shell, only 4 or 5 

 mm. high. In outline it is nearly square, and irom 

 the beak near one corner run about nine prominent 

 ribs. The shell is pearly within. It is found near 

 San Pedro. Dr. Carpenter considers it identical 

 with the Chinese shell, V . ornata^ D'Orb. 



