74 



fossils we are about to describe belong to the first divi- 

 sion. 



This shell affords an excellent example of a continuous 

 line of muscular impressions from the beaks along the line 

 of attachment of the mantle, forming a complete circuit; 

 they are very strong at the anterior edge, where they sup- 

 port the powerful muscles of the cylindrical foot, the rapid 

 action of which, when boring down into the sand, has been 

 so often remarked; the animal is said to descend some- 

 times two feet perpendicularly with great rapidity. 



There are several recent as well as fossil species, all of 

 which are littoral shells. Solen vagina, Linn., is the type 

 of the genus. 



SOLEN gracilis. 



TAB. DCXLL— /g^. L 



Spec. Char. Transversely linear, seven times as 

 wide as long, subcylindrical, slightly curved, 

 smooth; anterior portion separated by a direct 

 furrow, small but rather wide, its upper mar- 

 gin oblique ; the posterior extremity slightly 

 rounded. 



This is a pretty shell, much like the Ensis [Solen Ensis, 

 Linn.) of the British shores, but it is more convex; its 

 generic charactei's also distinguish it. It is one of the most 

 interesting among the many discoveries of new shells made 

 at the Barton Cliff by Mr. F. E. Edwards. Several spe- 

 cimens were picked up. 



Fig. a. is an enlarged representation of the hinge. 



