MARGARITANA. 



175 



Mija margartfifera? Lin., Dillwyn, Wood, &c. 



Margaritana margaritifera, Lka, Trans. Amor. Phil. Soc. vi. 135 ; Synops. 3d. cd. 43.3, 



where a full synonymy may be found. 

 Margaritana arcuatu, Stimpson, Shells of New iMigland, \5 (IS.'jl). — Conrad, Synops. 



in Proc. Ac. Nat. So. vi. 202. 



Shell transversely much elongated, ovate or Ijiidncy-shaped, thick 

 and strong ; beaks within the anterior fourth, scarcely rising above 

 the line of the hinge, very much eroded ; hinge and basal margins 

 usually curved, nearly parallel; nearly as broad l)efore as behind the 

 hinge, and rounded ; more pointed l)chind, and the tij) appears as if 

 slightly truncated ; surface somewluit waved by the lines of growth ; 

 epidermis close and smooth upon the disk, loosely wrinkled towards 

 the margin and posteriorly, color ])itchy-l)lack. Within smooth, 

 hluish-wliite, and sometimes tinted flesh-color at the centre ; nacre 

 not extending to the margin, leaving a greenish l)order. Cardinal 



M. arcuata. 



teeth two in the left valve, erect, strong, pyramidal, the posterior 

 one deeply grooved in front so as to form four or five denticles along 

 its edge ; one on the right valve, long, erect, a little twisted, deeply 

 grooved along its front, and with a pit each side, at base ; cavity of 

 the beaks shallow. Length, four and one half inches ; height, two 

 inches ; breadth, one and one fourth inches. 



Found in most running streams in the interior ; I have never 

 found it near the seaboard. 



It is a very common shell, and is at once known Ity its curved 

 form, dark color, and the want of a lateral tooth. It is the largest 

 fresh-water mussel we have. 



