96 INVERTEBRATA OF MASSACHUSETTS. 



It is distinguished from other North American species by the po- 

 sition of its beaks, its epidermis, its narrow area between the beaks, 

 and by its being equivalve. Its height increases posteriorly, so that 

 the interior of a valve has an ovate shape. 



Mr. Say remarks, that, when violently opened, an effusion of red 

 sanies issues ; and hence it has acquired the name of bloody clam. 



ARCA TRANSVERSA. 



Shell rhomboidal, with from thirty-two to thirty-Jive ribs ; beaks 

 at the anterior third of the series of teeth. 



State Coll., No. 187. Soc. Cab., No. 2337. 



Area transversa, SAY ; Journ. Acad. Nat. Sc., ii. 269. 



" Shell transversely oblong, rhomboidal, with from thirty-two 

 to thirty-five ribs placed at nearly the length of their own diam- 

 eters distant from each other. Apices separated by a long narrow 

 space, and situated at the termination of the posterior (anterior) 

 third of the length of the hinge margin ; extremities of the hinge 

 margin angulated ; anterior [posterior] edge, the superior half 

 rectilinear ; posterior [anterior] edge rounded ; inferior edge 

 nearly rectilinear, or very obtusely rounded ; on the hinge space, 

 one or two angulated lines are drawn from the apex diverging to 

 the hinge edge." Say. Length 1J inch, height 1 inch, breadth 

 1J inch. 



Found about the sands of Nantucket and Martha's Vineyard, 

 and it is said to be not uncommon in Buzzard's Bay. 



I have quoted the description by Mr. Say, above, merely inter- 

 changing the terms anterior and posterior, to accord with the parts of 

 the shell to which those terms are applied in other parts of the Re- 

 port. The position of the beaks distinguishes it from the preceding 

 species. 



GENUS NUCULA, LAM. 



Shell transverse, without an area for the ligament between the 

 beaks ; a straight series of teeth each side, forming an angle at a 

 spoon-shaped pit which separates them. 



