CHIEFLY OF THE UNITED STATES. 21 



RemarJcs. — Two specimens only of this species were submitted to me by Mr. 

 Wheatley. One is not quite so elliptical as the other. It is one of the complanatus 

 groupj and is nearly allied to Plantii, (nobis,) but is not so lenticular as that species, 

 nor is it of so regular an ellipse, the basal margin being nearly straight. In the 

 cardinal teeth the two species diflfer entirely, Plantii having the cardinal tooth double 

 in the left valve, while that tooth is tripartite in Gcistonensis, in which also these 

 teeth are larger. 



Unio Chathamensis. pi. 6, fig. 19. 



Testa liEvi, lato-elliptica, subcompressa, valde inaequilaterali, postice obtuse biangulata, antice rotundata; 

 valvulis subtenuibus, antice parum crassioribus ; natibus prominuHs ; epiderniide tenebroso-fusca vel 

 tenebroso-viridi, radiata; dentibus cardinalibus parvis, crenulatis, in utroque valvule duplicibus ; 

 lateralibus longis, lamellatis subrectisque ; margarita alba vel purpurea et valde iridescente. 



Shell smooth, widely elliptical, somewhat compressed, very inequilateral, obtusely 

 biangular behind, rounded before ; valves rather thin, somewhat thicker before ; 

 beaks a little jDrominent ; epidermis dark brown, or dark green, rayed ; cardinal teeth 

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

 straight; nacre white or purple and very iridescent. 

 Proc. Acad. Nat. Sci., 1863, p. 191. 



Hab. — Rocky Run, Chatham County, North Carolina, E. Emmons, M. D. ; and 

 James' River, near Richmond, Va., Maj. Le Conte. 



My cabinet and cabinet of Dr. Emmons. 

 Diam. -6, Length I'l, Breadth 2-1 inches. 



Shell smooth, widely elliptical, somewhat compressed, very inequilateral, obtusely 

 biangular behind, rounded before ; substance of the shell rather thin, slightly thicker 

 before ; beaks a little prominent ; ligament small and dark brown ; epidermis dark 

 brown or very dark green, much rayed and with distant marks of growth ; umbonial 

 slope slightly raised and obtusely angular ; posterior slope very narrow, slightly 

 carinate, with two impressed lines in each valve from the beaks to the posterior 

 margin; cardinal teeth small, crenulate, double in both valves; lateral teeth long, 

 lamellar and nearly straight ; anterior cicatrices distinct, small and well impressed ; 

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

 placed immediately over the cavity of the beaks; cavity of the shell shallow and 

 wide ; cavity of the beaks shallow and rounded ; nacre white or purple and very 

 iridescent. 



Remarlcs. — Only two specimens were received from Dr. Emmons of this species. 

 In outline it is near to Tuomeyi and inepfAis' {x\ohh) , but cannot be easily confounded 

 with either. It is smaller than the former and not so oblique, and it is larger than 

 the latter. Neither of the specimens were perfect enough at the beaks to show the 

 character of the undulations of the tips. 



