UNITED STATES AND ARCTIC AMERICA, 203 



with very distant marks of growth ; urabonial slope very low and very obtusely 

 angular ; posterior slope very much compressed, very dark and raised into a high 

 carina; cardinal teeth small, tuberculate and double in both valves; lateral teeth 

 very long, attenuate, lamellar and nearly straight ; anterior cicatrices distinct, large, 

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

 cicatrices deeply impressed, in a row across the centre of the cavity of the beaks ; 

 cavity of the shell very shallow and very wide ; cavity of the beaks very shallow 

 and obtusely angular ; nacre purple and iridescent. 



Remarks. — Several imperfect specimens were among the shells from Weldon. It 

 belongs to the great complanatus group, and closely resembles the compressed wide 

 varieties. It is nearly allied to Roanokensis, (nobis.) When I published the de- 

 scription of the macer in the Proc. Acad. Nat. Sci. I had not seen the specimen of 

 a single valve which Prof. Emmons since sent to me from the Neuse River near 

 Raleigh. This valve seems to be of the same species, but it is very much larger 

 and heavier, while the outline and general appearance is the same. This valve 

 has a very strong resemblance to Roanokensis, and it may prove to be of that species. 

 This species is so high on the posterior slope as to appear winged, and the young 

 take an obovate form. 



Unio contractus. PI. 29, fig. 272. 



Tests, laevi, elliptica, valde compressa, valde insequilatei'ali, postice subrotundatii ; valvulis teuuibus ; 

 uatibus depressis, ad apices undulatis ; epidermide tenebroso-fusca, obsolete radiata; dentibus 

 cardinalibus parvis, tuberculatis ; lateralibus longis, lamellatis rectisque ; margaritS, vel alba vel 

 purpurea et irideseente. 



Shell smooth, elliptical, very much compressed, very inequilateral, subrotund 

 behind; valves thin; beaks depressed, undulate at the tips ; epidermis dark brown, 

 obscurely radiate ; cardinal teeth small, tuberculate ; lateral teeth long, lamellar 

 and straight; nacre white or purple and iridescent. 

 Proc. Acad. Nat. Sci., 1857, p. 86. 



Hob. — Roanoke River, Weldon, North Carolina, Prof. E. Emmons. 



My cabinet and cabinet of Prof. Emmons. 

 Diam. "3, Length - 8, Breadth 1/7 inch. 



Shell smooth, elliptical, very much compressed, very inequilateral, subrotund 

 behind ; substance of the shell thin ; beaks depressed, undulate at the tips ; liga- 

 ment rather long, thin and light brown ; epidermis dark brown, striate, obscurely 

 rayed, with distant lines of growth ; umbonial slope very slightly raised, obscurely 

 angular ; posterior slope very much compressed, elevated into a carina ; cardinal 

 teeth small, tuberculate, crenulate and disposed to be double in both valves ; 

 lateral teeth long, lamellar and straight; anterior cicatrices distinct, small and 



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