NEW UNIONIDiE OF THE UNITED. STATES. 81 



Unio plancus. PI. 10, fig. 229. 



Testa laevi, obliquo-ovata, subcorapressa, postice biangulata, antiee rotundata, valde inaequilaterali ; valvulis 

 crassiusculis, antiee paulisper crassioribus ; natibus proiuinulis ; epidermide luteo-fusca, radiata ; den- 

 tibus cardinalibus parvis, ereetis, crenulatis, in utroque valvulo duplicibus ; lateralibus sublongis subrec- 

 tisque ; margarita cseruleo-alba et valde iridescente. 



Shell smooth, obliquely elliptical, somewhat compressed, biangular behind, rounded 

 before and very inequilateral ; valves somewhat thick, slightly thickened before ; beaks 

 a little prominent ; epidermis yellowish brown, radiated ; cardinal teeth small, erect, 

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

 bluish white and very iridescent. 



Proc. Acad. Nat. Sci. 1860, p. 307. 



Hab. — Coosa River, Wetumpka, Alabama. E. R. Showalter, M. D. 



My cabinet and cabinet of Dr. Showalter. 

 Diam. -6, Length 1, Breadth 1-6 inch. 



Shell smooth, obliquely elliptical, somewhat compressed, biangular behind, rounded 

 before and very inequilateral ; substance of the shell somewhat thick, slightly thick- 

 ened before ; beaks a little prominent ; ligament short and dark brown ; epidermis yel- 

 lowish brown, with rather regular rays nearly over the whole disk, but broader and 

 darker on the posterior slope, with rather distant marks of growth ; umbonial slope 

 but slightly raised and somewhat flattened ; posterior slope slightly carinate, with two 

 impressed lines on each valve from the beaks to the posterior margin ; cardinal teeth 

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

 anterior cicatrices distinct, rather small and well impressed ; posterior cicatrices con- 

 fluent and very slightly impressed ; dorsal cicatrices placed in the centre of the cavity 

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

 obtusely angular; nacre bluish white and very iridescent. 



Soft parts. — Branchial uterus not charged, but very minute ova were found in the 

 ovarium. Branchial large, nearly semicircular, inner ones much the larger, united the 

 whole length of abdominal sack. Palpi rather small, subangular, united one-third 

 down the posterior edges. Mantle very thin, thickened and colored on the inferior 

 edges, and furnished with dark brown papillae below the branchial opening. Branchial 

 opening rather large, with numerous nearly black papilla?. Anal opening rather large, 

 with very numerous, very small papilla? on the inner edges. Super-aiial opening 

 rather large, colored on the edges and united below; color of the mass dirty 

 white. 



RemarJcs. — There were three specimens of this small species received from Dr. 

 Showalter. They are nearly allied to simus (nobis), but it may be distinguished by 

 its being biangular behind, by the rays being larger and wider apart, by being a 



•21 



