310 NEW UNIONID^, MELANID^, ETC., 



and crenulate ; lateral teeth long, rather thick and oblique ; anterior cicatrices 

 distinct, rather large, corrugate and well impressed ; posterior cicatrices confluent, 

 large and very slightly impressed; dorsal cicatrices placed over the cavity of the 

 beaks ; cavity of the shell deep and rounded ; cavity of the beaks deep and 

 angular ; nacre silver-white, with a narrow reddish border beautifully iridescent. 



Remarlis. — I have nine specimens of this species before me, the youngest of which 

 is about one-fourtli grown. Four ai-e from the Brazos River, sent by Dr. Lincecum 

 to the Smithsonian Institution; the others many years since were sent to me by Prof. 

 Forshey. Until I received those collected by Dr. Lincecum, I was not entirely 

 satisfied as to their not being a variety of plicatus, Lesueur, to which this species is 

 closely allied. There are, however, several points which distinguish them. Brazos- 

 ensis is a more rounded shell, and is more tumid at the beaks. The color of the 

 epidermis is also very different, being disposed to be of a dark rubiginose color, and 

 where the epidermis is removed, particularly on the beaks, the color is a tint of 

 salmon. The marginal line beyond the nacre is reddish, which is not the case with 

 plicatus. The species herein described under the name oi Lincecumii, which came 

 with it, cannot be confounded with it, for Lincecumii is globose and usually has five 

 or six folds, while Brazosensis has a few very irregular ones. The marks of growth 

 of Brazosensis are few, distant and well-marked, usually being impressed, and thus 

 on the first growth giving it a tumid appearance. On the umbonial and posterior 

 slope there are usually three irregular raised lines, one of which cuts diagonally the 

 folds. The undulations of the tips are few, very small and subconcentric. 



Unio coevinus. pi. 48, fig. 123. 



Testa Irovi, elliptica, inflata, valde insequilaterali, antice et postice rotuudata; valvulis subcrassis, 

 antice crassioribus ; natibus vix prominentibus ; epidermide nigra, subsquamea, eradiata ; 

 dentibus cardinalibus parvissimis decussatisque ; lateralibus lougis subrectisque ; margarita alba 

 et valde iridescente. 



Shell smooth, elliptical, inflated, very inequilateral, rounded before and behind ; 

 valves somewhat thick, thicker before ; beaks scarcely prominent ; epidermis black, 

 subsquamose, without rays ; cardinal teeth very small and decussate ; lateral teeth 

 long and somewhat straight; nacre white and very iridescent. 

 Proc. Acad. Nat. Sci. 1868, p. 144. 



Eal. — Flint River, Geo., J. C. Plant and Dr. Neisler ; Darien ? J. H. Couper ; 

 Neuse River, Raleigh, N. C, Prof. Emmons. 



My cabinet. 

 Diam. -7, Length -8, Breadth 1-3 inch. 



Shell smooth, elliptical, inflated, very inequilateral, rounded before and behind; 

 substance of the shell somewhat thick, thicker before; beaks scarcely prominent; 



