ENTODESMA. 203 



on the shores of the San Francisco bay, and which 



lives along the whole line of 

 coast. In shape it is oblong, 

 bulged at one end; while at 

 the other it is narrow, thin 

 Fig- ^70. and crooked. The outer 



coat shows man)' concentric striae, but this is easily 

 rubbed off, revealing the inner layer of the shell, 

 w^hich is nacreous or pearly. Its length is an inch or 

 an inch and a half. 



Our next species is named Entodesma saxicola^ 

 Baird, En-to-dez'-ma sax-ik'-o-la. It is a singular 

 mollusk, living in holes of various shapes and taking 

 whatever form is most convenient. Its shell is oblong, 

 bulged at the hinge end, gaping beneath, and pro- 

 longed at the rear end into a somewhat irregular and 

 elastic tube composed chiefly of epidermis. The whole 

 shell is thin and is covered with a yellow epidermis; 

 internally a little ossicle or plate covers the hinge. 



The variety cylindrica has a thicker shell, is very 

 rough, and is somewhat wedge-shaped. Length about 

 an inch; northern. 



Entodes7na inflata^ Conr. , in-fla-'-ta, resembles the 

 last, but is smaller, thinner, and more irregular, and 

 is composed largely of epidermis. Narrow in front, 

 w4der and thinner behind; southern. 



Mytilinieria Niittalli^ Conr., ^lyt-il-i-me^-ri-a Nut- 

 talF-i, is a singular mollusk which may sometimes be 

 found imbedded in a soft substance, probably a kind 

 of sponge. The shell is very thin, white, covered 

 with a brown epidermis. There is an ossicle under 

 the hinge. In shape it resembles an inflated bladder, 

 with the spiral umbones at one end. Its height is 

 about one inch. 



