Mr. Barnes on the Genera Unio and Alasmodonta. 273 
Of this Ber pct shell we have — specimens ; ; 
Diam. *6 Len ngt th *625 Breadth 1°05 inch. 
"625 | Ari 
‘15 8 1 5 
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 somewhiat elevated ; anterior lunule oval-heart- 
shaped; posterior lunule not distinct; 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 lpngtu deal ribs 
which are beautifully dancaiieise by the strie and w 
passing over them, ribs projecting and forming a po a 
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. 
Remarx.—This shell resembles, in shape, the dlasmo- 
donta marginata, but it is a well characterized Unio 
26. Unio Nasurus.—Shell oblong-lanceolate, thin 
produced and pointed before, hinge margin ele- 
vated, compressed, carinate. 
Unio Nasutus, Mr. Say. 
American pr pass plate 4, fig. 1. 
Tnhabits the Delawar 
My Collection. 
Diam. -5 Length 1-0 Breadth 2°2. 
Shell thin and slender; disks compressed ; beaks depres- 
sed; ligament elevated afd 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 
Vor. VI.—No. 2. 35 
