TETRICOLA. 91 



and liasal marg'ins nearly parallel, and the extremity Lkintly 

 rounded and a little gaj)ing ; beaks elevated and inelined forwards ; 

 in front of tlieni is a sharply ovate lunule, distinctly delined, and 

 marked only by the lines of growth ; 

 behind them is a projecting liga- 

 ment of considerable length ; sur- 

 face coarsely marked by the stages 

 of growth, and covered with ele- 

 vated, radiating lines, various in 

 size and distance ; at the posterior p. phoimiifonnis. 



hinge margin they arc crowded 



and very faint, while anteriorly they are large and distant ; about 

 seven or eight of them arc more prominent than the rest, and the 

 lines of growth rise upon them into vaulted, toothlike scales ; hinge 

 margin very narrow ; teeth two in each valve, seeming to rise out 

 of the cavity of the l)eaks and curving upwards; in the right valve 

 one tooth is prominent and furrowed ; the other, arising a little be- 

 fore it, and a little deeper within the shell, is quite short ; in the 

 left valve is one large, |)rominent tooth, so dee{)ly divided as to re- 

 seml)le two, and directly behind it, diverging widely in the direction 

 of iha margin, is a thin, much elevated tooth. Muscular im])res- 

 sions fidnt, connected by a very deeply notched pallial imin-ession ; 

 furrows within answer to ribs without. Length, one and one fourth 

 inches ; height, seven tenths of an inch ; l)readth, three fifths of an 

 inch. I have seen one specimen two and one half inches long. 



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

 Ijeaches it is found al)undantly, imbedded in jutting fragments of a 

 marsh which once existed there, Itut which has been waslied away 

 by inroads of the sea, and now only an occasional ren:inant lifts its 

 head above the surrounding sand. Also found in great quantities 

 boring into hard Idue clay, at low-water mark, on Phillip's Beach. 

 Sable Island, rare ( Willis). 



Deshayes remarks that it is a very extraordinary shell on account 

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

 Pholas. To any one who has seen a Pholas, the reseml)lance 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. Rus- 

 sell, has two tubes or siphons extending from the longer end, united 



