78 MACTRAD^. 



less rapidly than the anterior part ; ends rounded ; beaks elevated, 

 not meeting, pointed, and inclined forwards; the regions before 

 and behind the beaks are broad, flattened, and more or less heart- 

 shaped, defined by slightly elevated ridges ; surface finely marked 



by the lines of growth, white, covered with a 

 F's- 3S9. thin, dirty-brown epidermis ; hinge strong, the 



pit for the cartilage l)eing a small recess pen- 

 etrating deeply into the beaks ; before it is a 

 strong, prominent V tooth, and on each side 

 of it, in the left valve, is a stout and promi- 

 ^.TaZraiis. ucut lateral tooth, and in the other a deep fossa 



with elevated sides to receive it ; cavity of the 

 beaks deep ; muscular impressions deep ; pallial impressions dis- 

 tinct, with a shallow sinus posteriorly ; interior clear glossy-white. 

 Length, half an inch; height, seven twentieths of an inch; breadth, 

 three tenths of an inch. 



The siphons of the animal are yellow, long, and slender, the 

 upper one with a short valve, and bluish above ; the lower one 

 fringed. 



The only places where I have found this shell living are the 

 inlets of the salt marshes between Roxbury and Boston. But all 

 the fiats which have been drained l)y the erection of the Milldam 

 have a layer of them just beneath the surface ; and vast numbers 

 were unearthed in throwing up the embankments for the railways 

 which cross them. They douljtless exist plentifully in the full 

 basin on the other side of the Milldam. They are found abun- 

 dantly at New Bedford also, and I know them to l)e common about 

 Rhode Island. Plentiful in coves near Lynn ; Charles River at 

 Brighton Bridge. Near Charleston, S. C, it is plentiful in sandy 

 mud flats. 



It assumes very various forms, depending mostly on age. When 

 young, the shell is thin, rather compressed, and the beaks are in- 

 conspicuous and touching each other. By age it becomes very 

 thick and turgid, the beaks elevated and widely separated, and 

 the height of the shell often equals its length. 



The small, deeply penetrating pit of the hinge is very peculiar. 



The dimensions of one from the track of the Providence Rail- 

 road is as follows: length, nine tenths of an inch; lieight, eight 

 tenths of an inch ; In-eadth, six tenths of an inch. It is repre- 

 sented at Figure 34 of the first edition. 



It is not likely to be mistaken for any other species. The young 



