96 OBSERVATIONS ON NAIADES, 



As far as I have been able to ascertain, it has not been described. 

 From the roughness of the beaks it might perhaps be thought to 

 be only a variety of corrugata (Lam.). On comparing the two spe- 

 cies, however, they will be found to be entirely distinct ; the corru- 

 gata being " ovato-rhombea," while the eseruleics is "angusto-ellip- 

 tica." In some specimens the nacre is slightly rose-coloured along the 

 basal margin. 



Unio Obesus. Plate XIII. fia;. 26 



S' 



Testa rhomhoides-ovata, obliquci, inaquilaterali, inflatd; valvulis subcrassis; na- 

 tibus prominulis; dentibus cardinalibus elevatis, compressis cristatisque; lateralibus 

 longis et curvatis; margaritd livido-albd. 



Shell ovate-rhomboidal, oblique, inequilateral, inflated ; valves somewhat thick; 

 beaks rather prominent; cardinal teeth elevated, compressed and crested; lateral 

 teeth long and curved; nacre livid white. 



Hab. York river, Vir., William Cooper. 



My Cabinet. 



Cabinet of Lyceum of Natural History of New York. 



Diam. 1-5, Length 2, Breadth 3-3 inches. 



Shell ovate-rhomboidal, oblique, inflated, angular behind ; substance 

 of the shell somewhat thick ; beaks rather prominent and placed near 

 the anterior margin ; posterior slope wide and furnished with two im- 

 pressed lines on each side ; ligament long and large ; epidermis fuscous 

 and much wrinkled ; rays obsolete ; cardinal teeth oblique, elevated, 

 lamellar, crested, deeply cleft in the left valve ; lateral teeth long, 

 curved and enlarged towards the posterior termination ; anterior cica- 

 trices distinct ; posterior cicatrices disposed to be distinct ; dorsal cica- 

 trices form a row across the cavity of the beaks ; cavity of the beaks 

 rounded and deep ; nacre livid white and iridescent on the posterior 

 margin. 



Remarks. — This is one of the specimens so disinterestedly contri- 

 buted to our Transactions by the Lyceum of Natural History of New 



