86 NEW UNIONID.E OF THE UNITED STATES. 



larger species, and not having a salmon colored nacre. It is also darker in the epi- 

 dermis, being inclined to reddish brown. 



Unio instrdctus. Pi. 10, fig. 230. 



Testa laevi, subtriangulari, subcompressa, inaequilaterali, postic^ subbiangulata, antice rotunda; valvulis 

 crassiusculis, antiee crassioribus ; Datibus prominentibus, ad apices rugoso-undulatis; epidermide 

 mellea, exilissime striata, eradiata ; dentibus cardinalibus parviusculis, striatis crenulatisque ; laterali- 

 bus subcurtis, striatis, obliquis subrectisque ; margarita argentea et iridescente. 



Shell smooth, subtriangular, rather compressed, inequilateral, subangular behind, 

 round before; valves rather thick, thicker before; beaks prominent, roughly undu- 

 late at the tips; epidermis honey yellow, very finely striate, without rays; cardinal 

 teeth rather small, striate and crenulate ; lateral teeth rather short, striate, oblique 

 and nearly straight ; nacre silver white and iridescent. 

 Proc. Acad. Nat. Sci. 1861, p. 59. 



Hob. — Cahawba Kiver, Alabama. E. R. Showalter, M. D. 



My cabinet and cabinet of Dr. Showalter. 

 Diam. -7, Length 1-1, Breadth 1-5 inch. 



Shell smooth, subtriangular, rather compressed, inequilateral, subbiangular behind, 

 round before ; substance of the shell somewhat thick, thicker before ; beaks promi- 

 nent, with two or three large undulations on each one ; ligament short, somewhat 

 thick and light brown ; epidermis honey yellow, very minutely and transversely 

 striate, without rays, with very distant, rather thin lines of growth ; urabonial slope 

 raised and rounded ; posterior slope rather narrow, elliptical, with a slightly impressed 

 line from the beaks to the posterior margin ; cardinal teeth rather small, striate and 

 crenulate ; lateral teeth rather short, striate, oblique, nearly straight and thickened at 

 the end ; anterior cicatrices confluent, rather large and deeply impressed ; posterior 

 cicatrices distinct, rather large and well impressed ; dorsal cicatrices placed over the 

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

 of the beaks rather shallow and angular ; nacre silver white and iridescent. 



Remarhs. — A single specimen only was received from Dr. Showalter. While, in 

 outline, it is nearly the same as favidens, Ben., and Barnesianus (nobis), it is entirely 

 diiferent in other characters, particularly in the very remarkable undulations of the 

 beaks, which are large and irregular. In its close, shining strise, it resembles striatus 

 (nobis), but it is lighter colored, and cannot be confounded with that species, which 

 is much smaller and more oval in outline. It also reminds one of some varieties of 

 younger coccineus, Hild., but it has no rays, as they usually have, and is lighter 

 in the epidermis, and totally different in the undulations of the beaks, coccineus having 

 only a few very small ones at the tips. 



