jV/r, Barnes on the Genera Unio and Alasmodonta. 273 



Of this remarkable shell we have four specimens ; 



Diam. -6 Length '625 Breadth 1'05 inch. 

 •625 -7 M 



•75 -8 15 



•8 -8 1-3 



Shell moderately thick, acutely angulated before obtuse 

 and somewhat angulated behind ; disks inflated; anterior 

 slope flattened and forming a right angle with the disk, rib- 

 bed longitudinally and wrinkled transversely ; beaks one 

 third from the posterior extremity, decorticated approxi- 

 mate and somewhat elevated ; anterior lunule oval-heart- 

 shaped ; posterior lunule not distinct j basal margin a 

 little depressed near the anterior extremity ; anterior mar- 

 gin straight, and its edge not entire ; epidermis yellowish- 

 green, rayed with dark green, finely striated transversely, 

 and with from three to six more conspicuous transverse 

 wrinkles. Anterior slope marked with longitudinal ribs 

 which are beautifully cancellated by the striae and wrinkles 

 passing over them, ribs projecting and forming a dentated 

 edge ; shell slightly gaping at both extremities ; cardinal 

 teeth two in each valve, compressed and crenulate, lamellar 

 teeth short, projecting, finely crenulate, and terminating ab- 

 ruptly ; naker bluish-white iridescent. 



Remark. — This shell resembles, in shape, the Alasmo- 

 donta margiiiata, but it is a well characterized Unio. 



26. Unio Nasutus. — Shell oblong-lanceolate, thin 

 produced and pointed before, hinge margin ele- 

 vated, compressed, carinate. 



Unio Nasutus. Mr. Say. 



American Conchology, plate 4, fig. 1. 



Inhabits the Delaware. 



My Collection. 



Diam. •S Length 1^0 Breadth 2^2. 



Shell thin and slender; disks compressed ; beaks depres- 

 sed ; ligament elevated and slender ; anterior lunule dis- 

 tinct, somewhat depressed at the margin, and with obsolete 

 longitudinal ribs; hinge margin straight; basal margin 

 nearly parallel with the hinge, slightly divergent ; anterior 



Vol. VI No. 2. 3.5 



