90 OBSERVATIONS ON NAIADES 



Unio Varicosus. Plate XL fig. 20. 



Testa subellipticd, obliqud, poslice compressd, varicibus transversis et concentricis 

 instructa; valvulis pracrassis ; natibus subterminalibus, prominentibus, incurvis ; 

 dentibus cardinalibusmodicis; later alibuslongis,magnis etsubrectis; margaritd alba. 



Shell subelliptical, oblique, compressed behind, varicose, wilhtransverse concentric 

 elevations; valves very thick; beaks nearly terminal, elevated, incurved ; cardinal 

 teeth rather small ; lateral teeth long, large and nearly straight ; nacre pearly white. 



Hab. Ohio river, T. G. Lea. 



My Cabinet. 



Cabinet of Prof, Vanuxem. 



Cabinet of P. H. Nicklin. 



Diam. 2-1, Length 3, Breadth 4-2 inches. 



Shell subelliptical, oblique, compressed and rounded behind, varicose 

 from near the beak to basal margin, with transverse concentric eleva- 

 tions along the lines of successive growth ; substance of the shell very 

 thick; beaks nearly terminal, elevated, incurved; ligament long and 

 large ; epidermis reddish brown ; cardinal tooth rather small, direction 

 same as lateral tooth, widely cleft in the left valve, in the right valve 

 emerging from a pit ; lateral teeth long, large and nearly straight ; an- 

 terior and posterior cicatrices both distinct ; dorsal cicatrices situated 

 on the lower part of the cardinal tooth, and on the under side of the 

 plate between the cardinal and lateral teeth ; cavity of the beaks rather 

 deep and rounded ; nacre pearly white. 



Remarks. — This species most resembles the U. Msopus (Green). It 

 differs from it, however, in being rounded behind, in the beaks being 

 nearly terminal, in the varices being less elevated and more trans- 

 verse; and in the absence of elevations along the umbonial slope. 

 There being no varicose undulations on young individuals, which are 

 generally obscurely radiated, it is difficult for the unpractised eye to 

 recognize the species to which they belong. 



