50 Bulletin 5 320 



144 FOSSIL SHELLS. 



ther large concentric wrinkles, and lines of growth ; 

 an elevated undulation on the anterior submargin, 

 marking the greatest length of the shell : umbones 

 not very prominent, apex rather suddenly incurv- 

 ed, acute ; impressed space behind the beaks, di- 

 lated and rather profound ; anterior tooth striated 

 externally, and placed on the middle of the ante- 

 rior margin. 



Large specimen, greatest length taken oblique- 

 ly, three inches and a half, breadth rather less. 



Small specimen, greatest length rather over one 

 inch and a half, breadth nearly one inch and four- 

 fifths. 



This shell is so much like the Venus rustica, 

 Sowerby, that I hesitated to give it a distinct 

 name. Besides being somewhat less transverse, 

 it may be remarked that the hinge groove, behind 

 the primary tooth, is much more elongated ; but 

 notwithstanding these differences, such is the ge- 

 neral correspondence of the two shells, that I 

 should not be surprised if this should prove to be 

 only a variety of the rustica. 



A large specimen which formerly belonged to 

 the collection of the late Professor B. S. Barton, 

 was presented to the Academy by Mr. Watson. 

 A smaller one was obtained by carefully dissect- 

 ing one of the friable masses containing fragments 

 of the Perna, in Mr. Finch's collection. 



[J. A. N. S., Phila., ist Ser., Vol. IV, 1824.] 



