CITAMA. 49 



Cpr., probably a variety of this species, is shorter 

 and broader, with a glossy epidermis. It may 

 be found near the entrance to the Golden Gate. 



Another mussel-like shell, shown in Fig. 2, PI, 

 XIII, is Septifer bifurcatus. Eve. Its generic 

 name, " partition bearer," was given from the 

 fact that a little, internal, shelly partition 

 stretches across each valve at the apex ; while 

 the specific name, " two-forked," refers to the ex- 

 ternal ribs by which the shell is marked, which 

 often divide into two. It is strong, white and 

 nacreous within, and covered with a dark epi- 

 dermis without ; the average length is one inch. 

 It may be found, at low tide, attached to the 

 rocks by a byssus. 



The next species, Chama pellucida, Sby., an 

 internal view of which is shown in Fig. 3, PL 

 XIII, might easily be overlooked when it is firm- 

 ly fastened to a rock. The outer surface is gray 

 or greenish, sometimes dashed with rosy red, 

 very rough, and marked by many close frills, 

 which are translucent, like chalcedony. The 

 hinge tooth is very strong, and the inside is lined 

 with a white, opaque layer, beautifully crenulated 

 at the edge. It grows from one to two inches in 

 diameter, and may be found at low tide, firmly 

 grown to the rocks, which must be broken to get 

 the entire shell. The name " Chama," is very 

 old, having been mentioned by Pliny. 



Quite unlike the Cham as are the Cockles, or 

 Heart-shells. Beautiful in outline, regular in 

 growth, and free to move, they but little resem- 

 ble their irregular, Imp-hazard, stationary neigh- 

 bors. The animal has a remarkably long foot, 



