﻿UNITED STATES. 77 



a young individual, but I cannot place it with any described species. The nacre is 

 slightly purple in the cavity of the beaks. The undulations of the beaks are uncom- 

 monly regular and very beautiful. In this specimen there are seven on each beak, 

 all regularly succeeding each other and forming an acute angle in the middle. 



Unto intercedens. PI. 15, fig. 57. 



Testa lsevi, elliptica, subinflata, valde inaequilaterali, postice subangulata ; valvulis subcrassis ; natibus 

 prominulis ; epidermide tenebroso-fusca; postice radiata, antice subsulcata ; dentibus cardinalibus 

 parvis, angulatis, in utroque valvulo duplicibus ; lateralibus longis, lamellatis subrectisque ; margarita 

 purpurea et iridescente. 



Shell smooth, elliptical, somewhat inflated, very inequilateral, subangular behind ; 



valves somewhat thick ; beaks a little prominent, epidermis dark brown, radiated 



behind and slightly furrowed before ; cardinal teeth small, angular, double in both 



valves ; lateral teeth long, lamellar and nearly straight ; nacre purple and iridescent. 



Proc. Acad. Nat. Sci. 1857, p. 32. 



Hah. — Streams near Columbus, Georgia. Bishop Elliott. 



My cabinet and cabinet of Bishop Elliott. 

 Diam. *8, Length 1-1, Breadth 1*9, inches. 



Shell smooth, elliptical, somewhat inflated, very inequilateral, obtusely angular 

 behind and rounded before ; substance of the shell somewhat thick, thicker before ; 

 beaks a little prominent, ligament rather long and thin ; epidermis dark brown, 

 obscurely radiated behind and slightly furrowed before with rather distant marks of 

 growth ; umbonial slope slightly elevated and rounded ; cardinal teeth small, angular, 

 double in both valves and crenulate ; lateral teeth long, lamellar and nearly straight ; 

 anterior cicatrices distinct and deeply impressed ; posterior cicatrices confluent ; dorsal 

 cicatrices placed in the centre of the cavity of the beaks ; cavity of the shell rather 

 shallow ; cavity of the beaks very shallow and subangular : nacre purple and 

 iridescent. 



Soft Parts. — A male. Branchiae large, rounded below, inner ones much the larger, 

 closed the whole length of abdominal sack. Palpi very large, thick, suboval, united 

 more than halfway down the posterior edges. Mantle thickened and double along the 

 edge, colored below the branchial opening where there are small somewhat distant 

 papillse. Branchial opening large, with numerous small brownish papillae on the inner 

 edges. Anal opening rather large, with minute papillse on the anterior edges. Sivper- 

 anal opening rather small, inner edges colored, united below for some distance. Color 

 of the mass whitish. 



Remarks. — A single specimen, a male, in alcohol and several dry ones were received 

 from Bishop Elliott. It belongs to the fallax group and inclines to subellipsis (nobis). 

 It differs from the latter in color of the nacre and in the rays. It is a more com- 



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