﻿TKUNCILLA 19 



what distinct from the rest of the shell : surface with uneven 

 concentric sculpture; epidermis pale brownish-green or brown- 

 ish, feebly rayed ; pseudocardinals ragged, double in the left 

 valve, single or treble in the right ; laterals short, granular, 

 more or less double in both valves ; muscle scars impressed ; 

 nacre white ; male shell subrhomboid, with a wide radial im- 

 pression in front of the posterior ridge and a strong radial 

 ridge in front of it ; female shell with an enormously produced 

 rounded wing-like marsupial swelling projecting downward 

 and slightly backward at or a little behind the middle of the 

 base. 



Length (male) 65, height 54, diam. 34 mm. 



Length (female) 66, height 48, diam. 45 mm. 



Length (female) 63. height 65, diam. 32 mm. 



Ohio River drainage. 



Type locality, Ohio. 

 Unio foliatus Hildreth, Am>. Jl. Sci. XIV, 1828, p. 284, fig. 



16. — Chenu, Man., 1859, II, p. 143, fig. 705. 

 Margarita (Unio) foliatus Li5a, Syn. 1836, p. 13; 1838, p. 14, 

 Margaron (Unio) foUatiis Lea, Syn. 1852, p. 20; 1870, p. 30. 

 Truncilla joliata Simpson, Syn., 1900, p. 521. 

 Unio Hcxtiosus Conrad, Monog., 1, 1835, p. 8, pi. iv^, fig. 2. — 



KusTER, Couch. Cab. Unio. 1852, pp. 46, 211, pis. ix, fig. 2; 



Lxx, fig. I. — Reeve, Conch. Icon., XVI, 1864, pi. vi, fig. 22; 



XIII, fig. 53. 

 Dysnomia Hexuosa Agassiz, Arch, fiir Naturg., I, 1852, p. 43. 



One of the most remarkable Naiades in the world. The male 

 and female shells are essentially alike until tbey are about one- 

 third grown, the wide, radial furrow of the male being a very 

 little deeper. At this period the female shell begins to develop 

 a rounded, prolonged marsupial swelling almost at the middle 

 of the base, which points slightly backward. This is sometimes 

 25 millimeters long and the same in width. It is scarcely, if 

 at all. radially sculptured, but becomes thin and wing-like as 

 it does in T. perplexa and gapes slightly. There is a more 

 decided gape at the extreme posterior part of the shell. In the 

 female shell the posterior scars are enlarged. 



