UNITED STATES. 38 



BemarJcs.— This is a species belonging to thecomplatiafas <^voui^, but it is usually wider, 

 more compressed, and is generally oblong until it is quite old, when it takes a more 

 oblique subtriangular outline -with a subemarginate base. Such is the form of the 

 specimen figured, which will In- recognized as including one of the various forms of 

 complanatus. The young have a very strong resemblance to strhjosm (nobis), and on 

 them may be observed very indistinct greenish rays. The undulations on the beaks 

 are very much like those of complanatus, but are more oblique. There is also a 

 strong resemblance in this species to Ro-noeUensis, described above, but it is more 

 compressed, and not so high on the uinbonial slope, nor is it so straight. I dedicate 

 this species to J. Postell, Esq., of St. Simon's Island, Georgia, to whom I am indebted 

 for many fine Georgia UnionUIa-. 



Uxio BuRKENSis. PI. 27, fig. 95. 



Testa Iscvi, transversa, comprcssa, ad latere planulata, inequilateral!, postici biangulata ; valvulis crassius- 

 culis; natibus prominulis; epiderraide fuseo-flavicante, micante, obsolete radiata; dentibus cardinalibiis 

 breviusculis, conipressis, acuniinatis ; latcralibus longis rectisque ; margaritS, purpurescente et irides- 

 centc. 



Shell smooth, transverse, compressed, flattened at the side, inequilateral and 

 biangular behind; valves somewhat thick; beaks slightly prominent; epidermis 

 yellowish brown, shining and obscurely radiated ; cardinal teeth rather short, com- 

 pressed, pointed ; lateral teeth long and straight; nacre purplish and iridescent. 

 I'roc. Acad. Nat. Sci., 1850, p. 112. 



iTij/^.—Buckhead Creek, Burke Co., Geo. Bishop Elliott. 



My cabinet and cabinet of Bishop Elliott. 

 Diam. "G, Length 1--5, Breadth 2-7 inches. 



Shell smooth, transverse, compressed, flattened' at the side, inequilateral, biangular 

 behind and obliquely rounded before; substance of the shell somewhat thick ; beaks 

 slightly prominent; ligament rather long, somewhat thick and lightish brown; 

 epidermis yellowish brown, shining on the sides, obscurely radiated, lines of growth 

 rather close and broad, between which the color on the .sides is yellowish ; umbonial 

 slope slightly raised and very obtusely angular; posterior slope raised into a moderate 

 carina, dark brown and slightly wrinkled ; cardinal teeth rather small, rather short, 

 compressed and pointed ; lateral teeth long, straight and lamellar; anterior cicatrices 

 distinct; posterior cicatrices confluent; dorsal cicatrices placed nearly in the centre 

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

 beaks very shallow, scarcely perceptible ; nacre light purple and iridescent. 



Remarks. — A single specimen only was received of Bishop Elliott. It is evidently 

 an adult. The beaks being eroded, the character of the tips cannot be given. Pro- 

 bably they are undulate like complanatus. The well defined double angle behind is 

 rather remarkable. It causes an emargination above. There is a disposition in the 



