﻿ALASMIDONTA 5°! 



resemblance to Unio hcterodon. It is however more regularly 

 rhomboid, higher, more iiiHated than that species and different- 

 ly colored. 



Group of Alasmidonta colUno. 



Shell rhomboid, subsolid, with beak sculpture consisting of 

 strong, concentric bars, sometimes slightly doubly looped, and 

 swollen on the low, posterior ridge; often with one or more 

 small spines on the disk in front of the posterior ridge; epi- 

 dermis brown, rayless or feebly rayed ; rest marks well de- 

 fined ; teeth rather compressed ; laterals lamellar. 



Animal unknown. 



Alasmjdonta collina (Conrad). 



Shell rhomboid, convex, subsolid, inequilateral, with mod- 

 erately full, high beaks, their sculpture a number of strong, 

 slightly double-looped ridges; posterior ridge full, rounded, 

 ending behind at the base of the shell in a rounded point ; 

 growth lines elevated into slight, concentric ridges; besides 

 this sculpture there are generally one or two sharp, prominent 

 tubercles or spines placed on a line running from the beaks to 

 a little behind the central base, though these are sometimes en- 

 tirely wanting ; epidermis smoky, greemish-brown, showing the 

 rest marks, subshining ; left valve with two subcompressed, ir- 

 regular pseudocardinals and two straight, delicate laterals; 

 right valve with a compressed pseudocardinal. with a vestigial 

 one in front of and behind it. with one lateral ; beak cavities 

 shallow; nacre bluish-white, slightly thicker at the anterior 

 base. 



Length 35, height 22. diam. without the spines 13, diameter 

 over all 15 mm. 



North Carolina and \Mrginia. 



Type locality, North River, A^a. 

 Unio colliniis Conrad, Monog., MIT. 1837. p. 65, pi. xxxvi. 



fig. 2; XII, 1840, p. 109, pi. i.x, fig. 3.— Hanley, Biv. Shells, 



1856, p. 382, pi. XX, fig. 57.— KusTER. Conch. Cab. Unio, 



t86t, p. 188, pi. ux, fig. 5. — SowERBv. Conch. Icon., XVI, 



i866. pi. xi.ix, fig. 263. 



