UNITED STATES AND ARCTIC AMERICA. 215 



Margaritana complanata, (nobis,) in Lake Winnipeg. The former being found, also in 

 Athabasca Lake, near the mouth of Moose River, Hudson Bay, on the upper waters 

 of the Missouri, in the St. Lawrence, Lake Champlain, in the Ohio River and the 

 upper waters of the Missouri. The latter in upper Missouri and the Ohio. (See 

 table of distribution of species, in Proc. Acad. Nat. Sciences, March, 1858.) Thus 

 luteolus is found in a southeast line of 3000 miles from Great Slave Lake to 

 Montreal, at four different points. And in a south direction about the same 

 distance to the Platte River and the Ohio. 



Anodonta Showalterii. PI. 33, fig. 284. 



Testa lsevi, elliptica, ventrieosS., postice obtuse angulata, antiee rotundata, subequilaterali ; valvulis 

 crassiusculis, antiee paulisper crassioribus j natibus subpromineutibus, ad apices minute undulatis; 

 epidermide tenebroso-fusca, obsolete radiata; rnargarita vel alba, vel paulisper salmonis colore 

 tincta et irideseente. 



Shell smooth, elliptical, ventricose, obtusely angular behind, rounded before and 

 nearly inequilateral ; valves somewhat thick, a little thicker before ; beaks some- 

 what prominent, minutely undulate at the tips; epidermis dark brown, obsoletely 

 radiate ; nacre white or slightly salmon color and iridescent. 

 Proc. Acad. Nat, ScL 1860, p. 307. 



Hab. — Coosa River, Wetumpka, Alabama, E. R. Showalter, M. D. 



My cabinet and cabinets of Dr. Showalter and Dr. Hartman. 

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



Shell smooth, elliptical, ventricose, obtusely angular behind, rounded before and 

 nearly equilateral, dorsal margin furnished with an imperfect tooth ; substance of 

 the shell somewhat thick, a little thicker before ; beaks somewhat prominent, 

 minutely undulate at the tips ; ligament rather large and dark brown ; epidermis 

 dark brown, obscurely rayed, and with very distant marks of growth ; umbonial 

 slope inflated and rounded ; posterior slope dark brown, very slightly raised, with 

 two indistinct lines from the beaks to posterior margin ; anterior cicatrices confluent 

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

 impressed ; dorsal cicatrices placed in a row anterior to the centre of the cavity of 

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

 and obtusely angular ; nacre white, or slightly salmon color and iridescent. 



Soft parts. — Branchial uterus filled with embryonic shells the whole length of the 

 outer leaves. Branchial rather large, nearly semicircular, thin, free half the length 

 of abdominal sack. Palpi rather large, subtriangular, united a short distance on the 

 posterior edges. Mantle very thin, slightly thickened on the edges, maculate on the 

 outer posterior edges. Branchial opening rather small, with numerous pale papillae. 

 Anal opening very small, with very small, pale papillae. Super-anal opening very 

 small, maculate on the outside and united for some distance below. Color of the 



mass dirty white. 



55 



