\EW UNIONID.K OF THE UNITED STATES. 73 



rcddisli yellow, without rays; cardinal teeth very thicl<, ol)tiisely conical and 

 corrugate ; lateral teeth very short, very oblique and straight ; nacre silver white and 

 iridescent. 



Proc. Acad. Nat. Sci. 18G1, p. 61. 



Hah. — Alabama River, Claiborne, Alabama; Judge Tait. Coosa River, Alabama; 

 E. R. Showalter, M. D. 



My cabinet and cabinet of Dr. Showalter. 

 Diam. 1-2, Length 1\S, Breadth 1-7 inch. 



Shell very tulierculate, subrotund, inflated, roundt'd before and behind, nearly 

 equilateral ; substance of the shell thick, thicker before ; beaks very prominent, 

 tumid ; ligament short, thick and dark brown ; epidermis reddish yellow, without 

 rays, darker on the anterior portion, with rather close lines of growth ; umbonial 

 slope raised and rounded ; posterior slope wide, cordate, very slightly raised and 

 usually covered with tubercles ; cardinal teeth very thick, obtusely conical and cor- 

 rugated ; lateral teeth very short, very oblique, straight and separated from the car- 

 dinal teeth by a broad plate, which extends towards the high beaks ; anterior cica- 

 trices distinct, small and very deeply impressed ; posterior cicatrices distinct, large and 

 well impressed ; dorsal cicatrices placed under the plate within the cavity of the beaks ; 

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

 nacre silver white and iridescent. 



BemarJcs. — A number of specimens of various ages were sent to me many years 

 since by my late friend. Judge Tait. I had always regarded them as belonging to 

 that group of which the well known and common species inistiilosus (nobis) may be con- 

 sidered the type, but I then had doubts whether they should be considered only as a 

 strong variety. On comparison with many hundred specimens of j>«5^«/o6?<« from many 

 widely separated habitats, and with some which inhabited the Alabama with them, 

 I am now satisfied that they diifer specifically. The pusiuhsit^ has a more or less 

 raised carina, which, in some cases, almost makes the outline of the plane of the disk 

 quadrate ; mperatm never has, but is always rounded, and is more elongate. 



Soft Parts. — A single specimen scarcely one-fourth grown, too young to decide on 

 the sex, was received recently from Dr. Showalter. As far as could be ascertained, 

 the various organs are very nearly the same as those of jjustulostis. Adults may be 

 found, when examined, to differ more, and the embryonic form also to differ ; but in 

 specie* so nearly allied as these are in the hard or enveloping parts, they would be 

 likely to resemble closely each other in the soft parts. 



Unio perpastus. pi. 7, fig. 219. 



Testa leevi, clliptica, vald6 ventricosa, vald^ ina3quilaterali, postice obtuse biangulata, antice oblique rotun- 

 data ; valvulis crassiusculis, anticc paulisper crassioribus ; natibus subprominentibus, inflatis ; opider- 



20 



