72 NKW UXIUNID.E OF THE 



Soft Parts. — Brancldal iiterm enormously large, filling quite the whole of the pos- 

 terior half of the outer branchiiB. This portion occupied by the branchial uterus is 

 nearly semicircular, being nine-tenths of an inch long and one and a half inches wide, 

 the inferior border being blackish. The branchial ovisacks in this specimen number 

 twenty-eight on each side, and some of them are one-eighth of an inch in thickness 

 and nine-tenths long. At the inferior end they are projected a quarter of an inch 

 beyond the line of the branchial membrane. In general character the branchial 

 ovisacks are like those of the well known cariosus, Say. BrancMce large, nearly 

 semicircular, inner ones larger in the anterior but smaller in the posterior portion of 

 the abdominal sack. Palin very large, oval, rather thick, oblique, and united only 

 at the upper part of the posterior edges. Mantle rather thin, with a very broad 

 palleal border, brown along the inferior edge and much thickened below the bran- 

 chial opening, extending to a large reddish brown flat, fleshy appendage on each side, 

 which is ramified into several points, flexile, extensile and retractile, the border 

 between which and the branchial opening is very much thickened, and colored 

 reddish brown. Branchial opening rather large, with numerous rather large, closely 

 set, brownish papilljB on the inner edges. Anal opening small, with very small 

 brownish papilla3 on the edges. Super-anal opening rather small, united for some 

 distance below, slightly colored on the edge. Color of the mass whitish. 



Embryonic shell ovato-pouch-shape ; color clear white. 



Remarks. — I have had a number of this species a long time in my possession from 

 Judge Tait and others, but considered it a well marked variety of ovatus, Say. But 

 those from Othcalooga Creek and Etowah River, subsequently received, satisfy me that 

 it is distinct. The specimen figured is a fine one from Othcalooga Creek, and among 

 the largest I have seen. The females are very much inflated. The younger speci- 

 mens have a very yellow, polished epidermis, with numerous distinct green rays 

 (sometimes interrupted,) over the whole disk. The posterior slope is very much flat- 

 tened, presenting a heart-shaped view, with a curved furrow on each side from beak 

 to posterior margin, where it is terminated by a well marked opening between the 

 valves. In some individuals the cardinal tooth of the right valve is disposed to be 

 tripartite. The nacre of some is quite pinkish on the posterior portion. The lateral 

 tooth of the right valve, always single, is enlarged at the posterior end and suddenly 

 terminated. 



Unio umbrans. pi. 13, fig. 53. 



Testa Iffivi, elliptica, ventricosa, subsequilaterali, postice obtuse angulata, compressS et emarginata ; valvulis 

 crassis, antice crassioribus ; natibus prominulis ; epiderraide tenebroso-fusca, postice obsolete radiata ; 

 dentibus cardinalibus subgrandibus, erectis, obtuso-conicis, in utroque valvulo duplicibus ; lateralibus 

 sublongis, subrcctis suberassisque ; margarita tenebroso-purpurea et iridescente. 

 Shell smooth, elliptical, ventricose, nearl}' equilateral, obtusely angular, com- 



