CHIEFLY OF THJE UNITED STATES. 307 



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

 angular behind and rounded before ; substance of the shell rather thin, thicker 

 before; beaks a little prominent, minutely undulate at tlie tijDs; ligament short, thin 

 and dark brown; epidermis reddish-yellow, very much radiated, with moderately 

 distant marks of growth; umbonial slope low and rounded; posterior slope narrow 

 elliptical; cardinal teeth small, erect and conical; lateral teeth long, lamellar and 

 somewhat curved; anterior cicatrices distinct, rather small and moderately well 

 impressed; posterior cicatrices confluent, large and slightly impressed; dorsal 

 cicatrices placed across the cavity of the beaks ; cavity of the shell shallow and 

 wide; cavity of the beaks shallow and obtusely angular; nacre salmon color and 

 very iridescent. 



BemarTcs. — A number of specimens of nearly all ages were sent to me by Major 

 Downie. In the color of the epidermis, as well as in the nacre, this species is nearly 

 allied to suhangulatus (nobis). In outline it is nearly the same, but sparus is rather 

 more transverse, and differs in not having a subangular umbonial slope. It also 

 differs in having smaller rays more closely set, and those more prevalent on the pos- 

 terior half of the disk. The nacre o? sparus is perhaps moi'e bi-illiant. Sparus cannot 

 be confounded with scituJus (nobis), although the two species are very nearly of the 

 same outline. Scitulus is rather heavier and larger, and has a yellow epidermis with 

 green rays, which are generally interrupted by the marks of growth. The nacre of 

 scitulus is usually white, with a slight tint of salmon in the cavity of the beaks, while 

 sparus is almost always dark salmon in the greater part of the cavity of the shell. 



Unio Copei. pi. 47, fig. 120. 



Testa Isevi, elliptica, subcompressa, insequilaterali, antice et postice rotundata; valvulis subcrassis, 

 antice crassioribus ; natibus prominuiis, ad apices undulatls ; epldermide tenebroso-fuscata, ad 

 marginem squamosa, eradiata; dentibus cardinalibus subcrassis, elevatis, compressis, corrugatis, 

 in utroque valvulo duplicibus ; lateralibus longis, lamellatis subcurvatisque ; margarita purpurea 

 et valde iridescente. 



Shell smooth, elliptical, somewhat compressed, inequilateral, rounded before and 

 behind ; valves somewhat thick, thicker before ; beaks slightly prominent, undulate 

 at the tips ; epidermis dark brown, squamose towards the margin, eradiate ; cardinal 

 teeth rather thick, raised, compressed, corrugate and double in both valves ; lateral 

 teeth long, lamellar and somewhat curved ; nacre purple and very iridescent. 

 Proc. Acad. Nat. Sci. 1868, p. 144. 



Hah. — Head-waters of the north branch of the Holston River, Smyth County, Va., 

 Prof. E. D. Cope. 



My cabinet and cabinet of the Academy of Natural Sciences. 

 Diam. -9, Length 1-6, Breadth 2-3 inches, 



74 



