64 TNVERTEBRATA OF MASSACHUSETTS. 



very short, and acutely rounded ; posteriorly very little narrowed, 

 the hinge and basal margins nearly parallel, and the extremity 

 bluntly rounded and a little gaping ; beaks elevated, and inclined 

 forwards ; in front of them is a sharply ovate lunule, distinctly 

 defined, and marked only by the lines of growth ; behind them is 

 a projecting ligament of considerable length ; surface coarsely 

 marked by the stages of growth, and covered with elevated, ra- 

 diating lines, various in size and distance ; at the posterior hinge 

 margin they are crowded and very faint, while anteriorly they are 

 large and distant ; about seven or eight of them are more prom- 

 inent than the rest, and the lines of growth rise upon them into 

 vaulted, tooth-like scales ; hinge margin very narrow ; teeth two 

 in each valve, seeming to arise out of the cavity of the beaks, 

 and curving upwards ; in the right valve one tooth is prominent 

 and furrowed ; the other, arising a little before it, and a little 

 deeper within the shell, is quite short ; in the left valve is one 

 large, prominent tooth, so deeply divided as to resemble two, 

 and directly behind it, diverging widely in the direction of the 

 margin, is a thin, much less elevated tooth. Muscular impres- 

 sions faint, connected by a very deeply notched palleal impres- 

 sion ; furrows within answer to the ribs without. Length 1| 

 inch, height j-^ inch, breadth j inch. 



Found on various parts of our coast ; at Chelsea and Nahant 

 beaches it is found abundantly, imbedded in jutting fragments of a 

 marsh which once existed there, but which has been washed away 

 by inroads of the sea, and now only an occasional remnant lifts its 

 head above the surrounding sand. Also in great quantities boring 

 into the hard blue clay, at low-water mark, on Phillips's Beach. 



Deshayes remarks, that this is a very extraordinary shell on ac- 

 count of its exterior aspect, which would lead one to mistake it for a 

 small Pholas. To any one who has seen a Pholas, the resemblance 

 is striking ; but the want of any wide gaping, and the articulated 

 hinge, at once correct the first impression. 



The teeth are so long and slender, that it is a rare thing to find a 

 specimen in which some of them are not fractured. 



The animal, according to the observations of the Rev. J. L. 

 Russell, has two tubes or siphons extending from the longer end, the 

 orifice of the one for imbibing water fringed with a circle of feathery 



