UNITED STATES AxND NORTHKRN MKXU (I 41 



Shell smooth, nearly roiiiid, somewhat inrtated, equilateral, slij^litly liattened over 

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

 before; beaks raised, with two 6r 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, Avith 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 cicatVices 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 and rounded; cavity of the beaks 

 deep and angular ; nacre silvery white and iridescent. 



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

 alcohol, but all had ova in the ovarium. Branchim 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 papillas on the inner edges. Anal opening small, apparently without papillas. 

 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 diflfers 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 

 petri)im that part is rounded. It belongs to the group of which U. circulm, (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 youngei' 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. G1, fig. 184. 



Testa laevi, elliptica, subcouipreisa, valdc ioaequilaterali, postic6 subangulata ; valvulis subteiiuibus, aiitiei- 



crassioribus ; nutibus prominulis, ad apices pereleganter et subcoocentrice undulatis ; epidermide teiie- 



brosooliva, polita, obsolete radiata; dentibus cardinalibus parvis, compressis, erectis crenulatisqae ; 



lateralibus longis, laniellatis subcurvisque; margaritii csDrnlea et vald6 irideseente. 



Shell smooth, elliptical, subcompressed, very inequilateral, subangnlar Iwhind ; 



valves rather thin, thicker before: hraks slir^htlv |ir.imiueul, very beautifully and 



