CHIEFLY OF THE UNITED STATES. 45 



Unio parvulus. pi. 16, fig. 43. 



Testa plicata, transversa, subinflata, ad latere eompressa, postice obtuse angulata, valde inaequilaterali ; 

 valvulis tenuibus, antioe aliquanto crassioribus ; natibus prominulis; epiderinide olivacea, subvlridi- 

 maculata ; dentibus cardinalibus parvis; compressis, crenulatis, in utroque valviilo duplicibus ; 

 lateralibus longis subrectisque ; niargarita cserulea et iridesceate. 



Shell plicate, transverse, somewhat inflated, compressed at the sides, obtusely 

 angular behind, very inequilateral ; valves thin, slightly thicker before ; beaks a 

 little prominent ; epidermis olivaceous, slightly green spot^d ; cardinal teeth small, 

 compressed, crenulate, double in both valves ; lateral teeth long and nearly straight ; 

 nacre bluish and iridescent. 



Proc. Acad. Nat. Sci., 1861, p. 307. 



Hah. — Coosa River, Alabama, E. R. Showalter, M. D. ; Chattanooga, Georgia, 

 A. Gerhardt. 



My cabinet and cabinets of Dr. Showalter and Smithsonian Institution. 

 Diam. -47, Length -75, Breadth 1-65 inches. 



Shell plicate, wnde, somewhat inflated, compressed at the side, obtusely angular 

 behind, very inequilateral ; substance of the shell thin, slightly thicker before ; 

 beaks a little prominent ; ligament rather short and light brown ; epidermis olive 

 green, with numerous minute angular markings over the disk, and with rather 

 distant marks of growth ; umbonial slope inflated and rounded ; posterior slope 

 slightly carinate and covered with curved folds; cardinal teeth small, compressed, 

 crenulate and double in both valves ; lateral teeth long and nearly straight ; 

 anterior cicatrices distinct, rather large and well impressed; posterior cicatrices 

 confluent, large and faintly impressed ; dorsal cicatrices placed across the centre of 

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

 beaks very shallow and slightly angular; nacre bluish, with a few salmon-colored 

 spots, and iridescent. 



Soft Parts. — Branchial uterus fully charged, having ten broad branchial ovisacks 

 pendent from the middle of the outer leaf, and occupying only one third of the 

 length. Branchia rather large, wide, curved below, inner one somewhat the larger, 

 free more than half the length of abdominal sack. Palpi very small, subtriangular, 

 united only at the superior portion. Mantle very thin, much thickened on the 

 posterior half of the margin, which is there crenulate and very dark colored. 

 Branchial opening small, with numerous light brown papillje. Anal opening rather 

 large, with very small light brown papillse on the inner edges. Sup)er-anal opening 

 small, lined with black and united below. Color of the mass whitish. 



Embryonic shell elongate-pouch shape, small, nearly the same with H. aculissimus, 



(nobis.) 



12 



