﻿UNITED STATES AND NORTHERN MEXICO. 359 



Shell smooth, nearly round, somewhat inflated, equilateral, slightly flattened over 

 the side and subemarginate at base; substance of the shell somewhat thick, thicker 

 before ; beaks raised, with two or three rather large irregular undulations at the tips ; 

 ligament short, rather thick and light brown ; epidermis smooth, striate on the 

 anterior slope, yellowish brown, without rays or obscurely rayed, with very distant 

 marks of growth ; umbonial slope raised into a very obtuse angle; posterior slope very 

 slightly raised ; with two or three obscure rays on each valve from beak to posterior 

 margin ; cardinal teeth large, erect, crenulate, and disposed to be double in the right as 

 it is in the left valve; anterior cicatrices distinct and well impressed; posterior cicatrices 

 nearly distinct ; dorsal cicatrices placed on the underside of the cardinal teeth ; palleal 

 cicatrix well impressed; cavity of the shell shallow aud rounded; cavity of the beaks 

 deep and angular ; nacre silvery white and iridescent. 



Soft parts. — Branchial uterus was not charged in any of the four specimens in 

 alcohol, but all had ova in the ovarium. Branchiae rather small, semicircular, inner 

 ones the larger, free more than one half the length of the abdominal sack. Palpi 

 large, subtriangular, united half way down the posterior edges. Mantle very thin, 

 with broad thickened edges. Branchial opening rather large, with a few very large 

 brown papillae on the inner edges. Anal opening small, apparently without papillae. 

 Super-anal opening long, slightly united below ; color of the mass whitish. 



Remarks. — I owe to the kindness of Dr. Moore, of Houston, the possession of two 

 specimens of the same size. They are young and probably only half grown. Subse- 

 quently I received four specimens from Prof. Forshey, one of which is adult. This 

 species is very nearly allied to U. petrinus, Gould. It differs in the beaks and pos- 

 terior slope which are not corrugate, simply having two or three folds at the tips. It 

 is not so high on the posterior slope, nor are the marks of growth so strongly ex- 

 hibited. In one shell there is a flattening before the umbonial slope, while in the 

 petrinus that part is rounded. It belongs to the group of which U. circulus, (nobis), may 

 be considered the type. The specimens from which the description is made are very 

 symmetrical in outline and thickness. They differ somewhat in the color of the epider- 

 mis, the younger ones being greenish yellow. On one of these, very obscure rays may 

 be seen while the other is devoid of them. The older ones are olive brown, and are 

 without rays. The smallest is 1*1 of an inch wide ; the largest 1-9 of an inch. 



Unio Texasensis. PI. 61, fig. 184. 



Testa laevi, elliptica, subcompressa, valde inaequilaterali, postice subangulata; valvulis subtenuibus, antice 

 crassioribus ; natibus prominulis, ad apices pereleganter et subconeentrice undulatis ; epidermide tene- 

 broso-oliva, polita, obsolete radiata ; dentibus cardinalibus parvis, compressis, erectis crenulatisque ; 

 lateralibus longis, lamellatis subcurvisque ; margarita cseralea et valde iridescente. 



Shell smooth, elliptical, subcompressed, very inequilateral, subangular behind; 

 valves rather thin, thicker before : beaks slightly prominent, very beautifully and 



