80 OBSERVATIONS ON NAIADES, 



thepustulatushavinga row, which resembles ihe cornutus in regularity. 

 These elevations however in the cornutus alternate in the two 

 valves, while in this species they are antagonist. In very perfect 

 young specimens, a minute tubercle may sometimes be observed on 

 the first growth. The elevations along the umbonial slope have more 

 resemblance to pustules, than those of the anterior row. 



Unio Lens. Plate VIII. fig. 10. 



Testa lenticulari, subventricosd, eequilaterali; valvulis suhcrassis; dentibus cardi- 

 nalibus magnis; lateralibus brevibus subrecHsque ; margaritd alba, raro rosed. 



Shell lenticular, subventricose, equilateral; valves somewhat thick ; cardinal teeth 

 large ; lateral teeth short and nearly straight ; nacre white, rarely rose coloured. 



jj^^ C Ohio, T. G. Lea. 



C Tennessee, Professor Vanuxem. 

 My Cabinet. 

 Cabinet of Prof. Vanuxem. 

 Cabinet of P. H. Nicklin. 

 Cabinet of H. C. Carey. 

 Diam. -6, Length -9, Breadth 1-2 inches. 



Shell lenticular, somewhat ventricose, equilateral ; substance of the 

 shell rather thick ; beaks slightly prominent, undulated at tip ; ligament 

 short and thick; epidermis smooth, anterior to the umbonial slope 

 brown, posterior yellowish ; cardinal teeth large and oblique, deeply 

 cleft in the left valve ; lateral teeth short and nearly straight, in the 

 left valve the superior division is much the smallest ; anterior cicatri- 

 ces distinct ; posterior cicatrices confluent ; dorsal cicatrices situated 

 on the under part of the cardinal tooth ; cavity of the beaks angular 

 and somewhat deep ; nacre white, pearly and iridescent, sometimes rose 

 coloured. 



Remarks. — This species very closely resembles the U. circulus 



