UNITED STATES AND ARCTIC AMERICA. 209 



rather small, compressed, double in both valves ; lateral teeth rather long, lamellar 

 and slightly curved ; nacre white and very iridescent. 

 Proc. Acad. Nat. Sci., 1862, p. 168. 



Hah. — Chattanooga, Georgia, Alexander Gerhardt. 



Cabinet of Smithsonian Institution. 

 Diam. 1, Length 1*8, Breadth 2-7 inches. 



Shell slightly sulcate, elliptical, rather compressed, sublenticular, obtusely angular 

 behind, round before ; substance of the shell somewhat thick, slightly thicker be- 

 fore ; beaks somewhat raised and approaching to medial ; ligament long, thick and 

 dark brown; epidermis straw yellow, with diverging capillary lines over nearly 

 the whole disk and with rather distant lines of growth ; umbonial slope slightly 

 raised and rounded ; posterior slope narrow-elliptical, somewhat carinate and 

 wrinkled ; cardinal teeth rather small, compressed, oblique and double in both 

 valves ; lateral teeth rather long, lamellar and slightly curved ; anterior cicatrices 

 distinct, large and well impressed ; posterior cicatrices distinct, large and mode- 

 rately impressed ; dorsal cicatrices placed on the upper side and within the cavity 

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

 shallow and obtusely angular; nacre white and very iridescent. 



Remarks. — A single specimen only of this species was sent by Mr. Gerhardt to 

 the Smithsonian. It is nearly allied to multiradiatus (nobis) in outline, color and 

 rays, but it differs in being sulcate on the anterior half, in being more compressed 

 and in having fewer and more distant capillary rays. The teeth are also more 

 compressed. The dorsal cicatrices are placed, in this specimen, on a small process 

 which extends behind the line of the lateral tooth. In the cavity of the beaks 

 the nacre is slightly salmon color, but this may not pervade all specimens. The 

 beaks are too much eroded to observe any undulations. I name this after Mr. 

 Alexander Gerhardt, of Whitfield County, Georgia, who has sent a number of fine 

 species from his zoological district. 



Unio Mercerii. PL 31, fig. 278. 



Testa lsevi, late elliptica, compressa, postice compressa et biangulata, antice rotundata, valde iusequi- 

 laterali ; valvulis subtenuibus ; natibus prominulis ; epiderraide tenebroso-fusca, subnitida, eradiata ; 

 dentibus cardinalibus parvis, tuberculatis striatisque ; lateralibus prselongis subeurvisque ; margarita 

 purpurea^ et valde iridescente. 



Shell smooth, broadly elliptical, compressed, biangular and compressed behind, 

 rounded before, very inequilateral ; beaks a little prominent ; epidermis dark brown, 

 somewhat shining, without rays; cardinal teeth small, tuberculate and striate; 

 lateral teeth very long and somewhat curved ; nacre purple and very iridescent. 

 Proc. Acad. Nat. Sci, 1862., p. 169. 



Rah. — Lee County, Georgia, Dr. Mercer. 



