UNITED STATES. 23 



distant. marks of growth; umbonial slope somewhat riiised and rounded; cardinal 

 teeth rather large, slightly elevated, striate and creiiulate ; lateral teeth short, thick, 

 granulate and somewhat curved; anterior cicatrices di.stinct and well impressed; 

 posterior cicatrices distinct and somewhat impressed ; dorsal cicatrices under the plate 

 behind the cardinal tooth ; cavity of the shell rather deep and irregularly rounded ; 

 cavity of the beaks rather shallow and very obtusely angular ; nacre white or pale 

 salmon color and iridescent. 



Soft parts. — Branchial uterus not charged, but ova were found in the ovarium. 

 Brandda' small, thin, nearly semicircular, inner one much the larger, free about half 

 the length of the abdominal sack. Palpi small and thin. Branchial opening small, 

 with small papilla) on the inner edges. Anal opening rather large, with numerous 

 very minute pai)illae. Super-anal opening long, seemed not to be united below, but 

 the specimen was torn in opening it. 



Remarhs. — A very small species, the figure nearly an inch and a half wide, being 

 made from the largest of seven or eight specimens which have come into my 

 possession. It usually has but two marks of growth, the half grown ones showing a 

 single well marked line. It is nearly allied to Ravenellianus (nobis) in outline and 

 in size. It is a little browner and more transverse, and the nacre is inclined to be 

 salmon color, which is not the case with Eavenellianus. The nacre is very much 

 thickened posteriorly, and the line of increase is marked by a thickening which 

 commences in the cavity of the beak, and sweeping round anteriorly, terminates 

 about the middle of the basal margin. 



Unio Roswellensis. pi. 24, fig. 87. 



Testa laevi, oblonga, subcompressa, ad latere compressa, postice biangulata, vald6 inaequilatcrali ; valvulis 

 snbcrassis; natibiis subpromincntibus ; epidermide tenebroso-fuscii, striata ; dentibus cardinalibu.s sub- 

 grandibus, crcDulatis, in utroque valvule subduplicibus ; lateralibus prrclongis subrectisque ; margarita 

 vel purpured vel salmonis colore tinctS, et valdfe iridescente. 



Shell smooth, oblong, rather compressed, biangular behind ; flat at the sides, very 

 inequilateral ; valves rather thick, beaks rather prominent ; epidermis dark brown, 

 striate ; cardinal teeth rather large, crenulate and somewhat double in both valves ; 

 lateral teeth very long and nearly straight ; nacre either purple or salmon color and 

 very iridescent. 



Proc. Acad. Nat. Sci., 1858, p. 165 



Hab. — Chattahoochee River, at Roswell, Cobb County, Georgia. N. A. Pratt, Jr. 



My cabinet and cabinet of Mr. Pratt. 

 Diam. -8, Length 1-5, Breadth 3-1 inches. 



Shell smooth, oblong, rather compressed, biangular behind, flat at the sides, very 

 inequilateral, broadly rounded before ; sub.-<tance of the shell rather thick ; beaks 

 rather prominent ; ligament long, somewhat thick and light brown ; epideiTnis dark 



