306 MARINE SHELLS 



more abruptly truncated before, smaller, and the 

 longitudinal lines are more indented. I have no 

 doubt but this species has been regarded, by authors, 

 as the same with trunculus, if so, judging by an in- 

 dividual of that species in the collection of the Aca- 

 demy, at least two distinct species have been con- 

 founded together under that common name. 



2. D. *fossor. Shell subtriangular ; anterior margin 

 short and rounded ; posterior hinge slope rectilinear ; 

 base very slightly prominent beyond a regular curve 

 at the middle ; valves longitudinally striated with 

 numerous, equal, parallel, regular impressed lines, 

 not visible to the unassisted eye, and obsolete on the 

 posterior margin; basal edge within crenate ; colour 

 pale-livid, with two longitudinal whitish rays before 

 the middle, both within and without. 



Var. a. Whitish. Var. b. Yellowish. 



Breadth from half an inch to three-fifths. 



Inhabits the coasts of New Jersey and Maryland. 



Cabinet of the Academy and Philadelphia Mu- 

 seum. 



Very numerous under the surface of the sand, 

 which is exposed at the recess of the tide. A wave 

 by removing the surface of the sand, exposes a great 

 many individuals to view, at its refluence, these im- 

 mediately penetrate the sand, and before the recur- 

 rence of the surge they are concealed. 



They are preyed upou by several shore birds and 

 fish ; the drum (Scisena chromis) and sheep's-head, 

 4 Spams ovicephalus) are sometimes caught in the 



