212 NEW UNIONIDiE OF THE 



scurely radiate, with rather distant lines of growth; umbonial slope raised and 

 obtusely angular ; posterior slope raised, with two obscure, impressed lines in each 

 valve, from the • beaks to the margin ; cardinal teeth small, rather compressed 

 and single in both valves ; anterior cicatrices distinct, very large and well impressed ; 

 posterior cicatrices confluent, large and slightly impressed; dorsal cicatrices well 

 impressed, and placed over and before the centre of the cavity of the beaks ; cavity 

 of the shell deep and wide ; cavity of the beaks shallow and obtusely angular ; nacre 

 white, bordered with purplish. 



Remarks. — This is a very interesting species, discovered by Dr. Gesner recently 

 in Alabama. It is very distinct from any species heretofore known in this country. 

 The cardinal teeth are rather more developed than in M. Elliottii, (nobis.) In the 

 five specimens before me, four have a purplish margin, which even shews under 

 the nacreous matter on the edge. The epidermis has a fine natural polish. I have 

 great pleasure in naming this fine species after the discover, — Dr. Gesner. 



Anodonta Simpsoniana. PI. 32, fig. 281. 



Testa kevi, elliptica, subcompressa, elongato-lenticulari, postice obtuse angulata, antice rotunda; 

 valvulis tenuibus ; natibus proniinulis, ad apices undulatis ; epidermide tenebroso-fusca, eradiata ; 

 uiargarita eseruleo-alba, et iridescente. 



Shell smoth, elliptical, rather compressed, elongately lenticular, obtusely angular 

 behind ; valves thin ; beaks a little prominent, undulate at the tips ; epidermis 

 dark brown, without rays ; nacre bluish white and iridescent. 



Proc. Acad. Nat. Sci., 1861, p. 56. 



Sab. — Fort Rae, Great Slave Lake, Arctic America, R. Kennicott. 



My cabinet. 

 Diam. 5, Length 1, Breadth 1-8 inch. 



Shell smooth, elliptical, somewhat compressed, elongately lenticular, obtusely 

 angular behind, round before ; substance of the shell thin ; beaks slightly pro- 

 minent, undulate at the tips ; ligament rather short and dark brown ; epidermis 

 dark brown, without rays, with regular, rather close well marked lines of growth ; 

 umbonial slope slightly raised and rounded; posterior slope very narrow-elliptical, 

 somewhat carinate ; anterior cicatrices confluent, large and very slightly impressed ; 

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

 placed above the centre of the cavity of the beaks ; cavity of the shell very 

 shallow and wide ; cavity of the beaks very small and subangular ; nacre bluish 

 white and iridescent. 



Remarks. — A single specimen only was received from Mr. Kennicott, and it 

 may not be full grown. It is far from being perfect, and the beaks are much 

 eroded. Enough remains, however, to be able to count four rather coarse undu- 



