CHIEFLY OF THE UNITED STATES. 27 



confluent ; dorsal cicatrices placed in the ujDper part of the cavity of the beaks ; cavity 

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

 nacre bluish white and iridescent. 



Bemarlcs. — This species has very much the general appearance of Williamsii, from 

 Virginia, herein described, but it is a smaller species, not so much inflated and is more 

 inequilateral. It is named after Lieut. Beale, U. S. Army, who obtained it in Texas 

 with several other fresh water Mollusca. 



Specimens were subsequently received from Mr. F. Hawn, of a larger size and 

 somewhat thicker. These show a slight thickening on the anterior basal portion of 

 the valves. The largest of Mr. Hawn's specimens is 5^ by 3 inches. He sent to me 

 besides this new species the following Urdonidce, which show a striking similax'ity to 

 the Ohio River basin, viz. : U. solidus, U. gibhosus, U. undulatus, U. luteolus, U. meta- 

 never, U. cornuius, U. rubiginosus, U. aureus, IT. tuberculaius, U. parvus, U. Ruter- 

 villetvsis, U. rectus, U. OGoidens, U. purpuratus, Margaritana compilanata, M. marginata 

 and Anodonia edentula. 



Anodonta Williamsii. PI. 10, fig. 26. 



Testa Isevi, ovato-oblonga, inflata, subaequilaterali, postiee subbiangulata, antice rotundata et aliquanto sul- 

 cata; valvulis subtenuibus, antice ad marginem incrassatis; natibus prominulis, inflatis, ad apices un- 

 dulatis ; epidermide vel viridi vel luteo-oliva, fulgida, obsolete radiata vel eradiata ; margarita cseru- 

 leo-alba et valde iridescente. 



Shell smooth, ovately oblong, inflated, subequilateral, subbiangular behind, rounded 

 and somewhat sulcate before ; valves rather thin, thickened before towards the 

 margin ; beaks a little prominent, inflated, undulate at the tips ; epidermis green or 

 yellowish olive, shining, obscurely radiate or without rays ; nacre bluish white and 

 very iridescent. 



Proc. Acad. Nat. Sci., 1862, p. 169. 



nab. — Potomac River at the "White House, below Mt. Vernon, H. C. Williams ; 

 Othcalooga Creek, Georgia, Bishop Elliott. 



My cabinet and cabinets of Smithsonian Institution and Bishop Elliott. 

 Diam. 1-6, Length 2-1, Breadth 3'8 inches. 



Shell smooth, ovately oblong, inflated, nearly equilateral, subbiangular behind, 

 rounded and somewhat sulcate before ; substance of the shell rather thin, thickened 

 before towards the margin ; beaks a little prominent, inflated, undulate at the tips ; 

 ligament long, thin and light brown ; epidermis green, or yellowish olive, shining, ob- 

 scurely radiate or without rays, having very distant marks of growth ; umbonial 

 slope flattened ; posterior slope wide, carinate, with three slightly raised lines and 

 rays from the beaks to the margin on each valve ; anterior cicatrices distinct, large 

 and slightly impressed ; posterior cicatrices confluent, large and very slightly im- 



