﻿292 OBOVARIA 



with a ravless. dusky hrowii, often cloth-like epidermis, which 

 is much lighter colored on the posterior slope; left valve with 

 two stout, radial pseudocardinals and two short, nearly 

 straight laterals ; right valve with three pseudocardinals, the 

 middle one strong, the hinder faint and sometimes wanting; 

 beak cavities shallow or only moderately deep, compressed ; 

 dorsal scars under the i>seudocardinals ; nacre silvery white, 

 pink, salmon, rich purple. 



Length 45, height 47, diam. 30 mm. 



Length 48, height 46, diam. 28 mm. 



Length 58, height 55. diam. 42 mm. 



( )hio, Tennessee and Cumberland River systems ; southeast 

 Louisiana and Tombigbee drainage. Reported from Mich- 

 igan and the St. Lawrence drainage. 



Type locality, the Ohio at Cincinnati, tiie Monongahela at 

 Pittsburgh and the Tennessee at Nashville. 

 Unio chxnlus Lea, Tr. Am. Phil. Soc, IIL 1829, p. 433. pi. 



IX, fig. 14 ; Obs., L 1834, p. 47. pi. IX, fig. 14. — Hanley, Biv. 



Shells, 1843. P- 201, pi. XX, fig. 23. — KusTER, Conch. Cab. 



L^nio, 1852, p. 41, pi. VIII, fig. 2. — Chenu, 111. Conch., 1858, 



pi. XVI, figs. I, I a, ih. — Reeve, Conch. Icon.. XVL 1865. 



])!. xx\ii, fig. 135. 

 Marii^arita (Unio) circulus Lea, Syn.. 1836, p. 33; 1838, p. 22. 

 Margaron (Unio) circulus Lea, Syn.. 1852, p. 34; 1870, p. 55. 

 OboT'oria circulus Simpson, Syn.. 1900. p. 600. 

 CJiiio subrotundus Ferussac, part, Guer. Mag., 1835, p. 28. 

 Unio subrotundus Raf. v. circulus P.^-tei.. Conch. Sam., IIL 



1890, p. 168. 

 Mya rotunda Wood. Index Test. (Rev.), 1856. p. 199. pi. i, 



Supp., fig. I. 



A remarkably variable and unsatisfactory s])ecies. Speci- 

 mens on the one hand almost run into retusa and on the other 

 hand there seems to be a more or less complete blending into 

 lens. Generallv it is smaller and more inflated than the latter 

 species. The epidermis of circulus on the body of the shell is 

 dark and absolutely lusterless ; that of lens is lighter colored 

 and of a more nearly uniform color, and often faintly shining. 



