﻿OP.OVARIA 



291 



mens, rayless ; left valve with two stout subradial pseudo- 

 cardinals, with two short, curved laterals, the lower sometimes 

 double ; right valve with three pseudocardinals, the middle the 

 larg-er, the hinder parallel with the somewhat double lateral ; 

 hinge plate flat, sharply curved in front of the laterals ; beak 

 cavities deep, compressed, the dorsal scars under the pseudo- 

 cardinals ; muscle scars deep, small ; nacre coppery-purple, 

 that of the female thickened in front. Female shell with a 

 decided groove behind the posterior ridge, the marsupial area 

 slightly produced. 



Length (male) 50, height 50, diam. 32 mm. 



Length (female) 47, height 53, diam, diam. 35 mm. 



Ohio, Cumberland, and Tennessee Kiver systems. 



Type locality, "les rknercs de la Kom'elle Ecossc." 

 Unio rctusa Lam.\rck, An. sans A'ert., VL 1819, p. yi. 

 Unio rctnsus Conrad, Monog., II, 1836, p. 19, pi. viii. — Reeve, 



Conch. Syst., L 1841, p. 118, pi. i.xxxviii, fig. 16. — Hani.ey, 



Biv. Shells, 1843, P- 202, pi. xxi, fig. 11. — Kuster, Conch. 



Cab. Unio. 1852, p. 58, pi. xiii, fig. 2.— Sowerby, Conch. 



Icon., XVL 1868, pi. Lxxi, fig. 363.— QAhh, Tr. Acad. 



Sci. St. Louis, Vn. 1895, P- 45- pl- vm. 

 Margarita (Unio) rctnsus Lea, Syn., 1836, p. 34; 1838, p. 23. 

 Margaron (Unio) rctnsus Lea, Syn., 1852, p. 35; 1870, p. 56. 

 Obo7'aria rctusa Simpson, Syn., 1900, p. 5C79. — Ortmann, 



Ann. Car. Mus., \^IIL 1912, p. 321, fig. 20. 

 Unio torsns Potiez and Michaud, Gall. Moll.. 1844, P- I49- 



pi. LVII, figs. I, 2. 



A most remarkable shell, the beaks in old specimens being 

 very high and curved forward like those of an Isocardia. 



OnovARiA ciRcui.us (Lea). 



Shell variable in outline, subtriangular, rounded or short 

 elliptical, solid, inflated, with high beaks, which are often 

 somewhat turned forward over a moderate lunule, their sculp- 

 ture consisting of a few rather feeble, slightly doubly-looped 

 ridges ; posterior ridge low, rather rounded ; surface smooth 

 or having few low, irregular, wide, concentric ridges, covered 



