CHIEFLY OF THE UNITED STATES. 17 



Shell smooth, triangular, inflated, flattened at the sides, very inequilateral, sub- 

 biangular behind, rounded before ; valves thin ; beaks prominent ; epidermis brown- 

 ish green or olivaceous, obscurely rayed ; cardinal teeth very small, compressed, 

 oblique, double in both valves ; lateral teeth long, lamellar and straight ; nacre 

 bluish white and iridescent. 



Proo. Acad. Nat. Sci. 1863, p. 193. 



Hah. — Waccamaw Lake, North Carolina, E. Emmons, M. D. 



My cabinet and cabinet of Mr. Emmons. 

 Diam. 'G, Length '7, Breadth 1'4 inches. 



Shell smooth, triangular, inflated, flattened at the sides, very inequilateral, some, 

 what biangular behind, rounded before ; substance of the shell thin ; beaks promi- 

 nent ; ligament short, thin and brown ; epidermis brownish green or olivaceous, 

 obscurely rayed and with distant marks of growth ; umbonial slope very much 

 raised and sharply angular ; posterior slope wide, flattened and somewhat carinate ; 

 cardinal teeth very small, compressed, oblique and double in both valves ; lateral 

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

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

 dorsal cicatrices placed above the centre of the cavity of the beaks ; cavity of the 

 shell rather deep and wide,- and showing the angle of the umbonial slope; cavity of 

 the beaks rather deep and angular; nacre bluish white and iridescent. 



Remarks. — Only two specimens and a few odd valves were received from Dr. 

 Emmons. It is to be regretted that more were not obtained, as none of them are 

 very perfect, the beaks of all being more or less imperfect, and none affording the 

 character of the undulations of the tips, if there be any. This is a well character- 

 ized species, and in the outline and high angular umbonial slope closely resembles 

 triangularis Bar., but it differs totally in the coloring of the epidermis, the beautiful 

 arrowheaded marks on triangularis being replaced in this shell by obscure thin rays. 

 In the substance of the shell they also differ, Waccamawensis being thin, while tri- 

 angularis is a thick shell. 



Unio Mecklenbergensis. PL 5. fig. 15. 



Testa Isevi, elliptica, subcompressa, inge([uilaterali, ad latere parum planulata, postice biaogulata, antice 

 rotundata; valvulis crassis, antice crassioribus ; natibus prominulis; epidermide tenebroso-fusca, 

 obsolete radiata ; dentibus cardinalibus subgrandibus, striatis crenulatisque ; lateralibus longis, 

 lamellatis corrugatisque ; margarita albida vel purpurea et valde iridesceate. 



Shell smooth, elliptical, somewhat compressed, inequilateral, somewhat flattened at 

 the side, biangular behind and rounded before; valves thick, thicker before ; beaks a 

 little prominent ; epidermis dark brown, obscurely rayed ; cardinal teeth rather 



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