42 



neiform, and produced posteriorly; the rays confined 

 to the umbo and obsolete. Inhabits the Alabama 

 and Black Warrior rivers. 



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UNIO DILATATUS. 



Plate XXI. 



DESCRIPTION. 



Shell ovato-elliptical, thick and ponderous, slightly 

 sinuous; posterior side produced, compressed, cunei- 

 form; umbo broad, flattened, summit obtusely round- 

 ed; anterior lunule large, elliptical; umbonial slope 

 angulated, not very distant from the margin; basal 

 margin slightly contracted near the middle; within 

 obliquely sulcated from the umbo towards the poste- 

 rior basal margin; colour purple, with a bluish mar- 

 gin; cardinal teeth thick, direct; lateral teeth very 

 thick, and terminating rather abruptly. 



SYNONYMES. 



U. dilatatus, Ruf. Ann. gen. des Sc. Phys. vol. v. p. 31. Poul- 

 son's trans, p. 25. Say, Amer. Conch. No. 6. Ferr. Mag. de 

 Zool. 



U. nasutus, Lam. An. sans vert. vol. vi. p. 75. 



U. gibbosus, Barnes. Silliman's Journ. vol. vi. p. 262. 



Cab. A. N. S. No. 1072. 



OBSERVATIONS. 



In outline this species approaches U. fasciolaris, 

 but "differs in the much less dilated cardinal plate, in 

 having the anterior [posterior] smaller muscular im- 



