﻿PTYCHOBRANCHUS 335 



Var. cauiclus (Lea). 



Shell solider, more inflated and much more arched or hump- 

 ed dorsally than the type. 



Type locality, Ohio River. 

 Ufno camelus Lea, Tr. Am. T'hil. Soc, V, 1834, p. 102, pi. xv,. 



fig-. 45; Obs., I, 1834, p. 214. pi. XV, fig-. 45. — Hanley, Biv. 



Shells, 1843, p. 184. pi. XXI, fig. 54. — SowERHY, Conch. Icon., 



XVI, 1867, pi. LV, fig. 283. 

 Margarita (Unio) camelus Lea, Syn., 1836, p. 19; 1838, ]). 17. 

 Margaron (Unio) camelus IvEa, Syn., 1852, p. 24; 1870. p. 37. 



The variety is quite differently shaped from the type, but 

 there is a complete connection of the two by intermediate spec- 

 imens. The humped character is shown in the young shells 

 as well as in the adults. 



The species is a variable one in form and color. Specimens 

 from Arkansas show somewhat linear rays and approach P. 

 clintonense. Old shells are sometimes decidedly arcuate, es- 

 pecially in the variety. 



PTYCHOBRANCHUS CLINTONENSE Simpson. 



Shell oblong, ovate, elliptical or subrhomboid, sometimes 

 Subtriangular, solid, scarcely inflated, rather wider behind ; pos- 

 terior ridge feeble, rounded or slightly double, ending behind 

 in a faint biangiilation ; beaks low and not inflated, their sculp- 

 ture not seen ; surface nearly smooth, yellowish-green covered 

 with delicate, wavy, green, faint rays ; epidermis silky when 

 fresh, but nearly smooth when rubbed : hinge solid ; left valve 

 with two low, small, solid pseudocardinals, the hinder larger 

 and sometimes dentilate, with two remote laterals ; right valve 

 with one pseudocardinal and a vestigial one on each side of it, 

 with one, sometimes more or less double, lateral ; beak cavities 

 shallow ; muscle scars smooth and impressed ; nacre bluish- 

 white, often with lurid blotches, thicker in front. 



Lenj^h 90. height 47, diam. 28 mm. 



Little Red River, Arkansas : Indian Territory ( ?) ; south- 

 west Tennessee (?). 



