﻿T.AMPSILIS 39 



There are two, somewhat compressed pseudocardinals in the 

 left valve, one in front of the other, the hinder high and hav- 

 ing a triangular outline, the front lower, and both of these are 

 in front of the beak ; the hinge plate is narrow and rounded 

 behind them, and there are two rather short, slender laterals ; 

 right valve with two compressed pseudocardinals, the lower 

 the higher, separated by a deep, nearly parallel-sided socket, 

 and one high, curved lateral, which is sharply truncated behind ; 

 beak cavities deep and wide ; muscle scars not deep, smooth, 

 the hinder semicircular; nacre brilliant, silvery, bluish-white 

 or sometimes a beautiful pink. 



In the female shell the marsupial swelling is pronounced, 

 and the shell is generally higher than that of the male. 



Length 130, height 90, diam. 60 mm. 



Entire Mississippi drainage ; St. Lawrence system ; Nelson 

 River and tributaries. 



Type locality, Wisconsin River ; Mississippi River, Prairie 

 du Chien, Wis. 

 Unio ventricosus Barnes, Am. Jl. Sci. VL 1823, p. 267, pi. 



XIII, fig. 14 (outline). — Say, Am. Conch., No. IV, 1832. pi. 



XXXII. — HANI.EY, Biv. Shells, 1843, p. 189, pi. xxiv, fig. 8. 



— Chenu, Bib. Conch., ist ser. Ill, 1845, P- 45» pl- xii, figs. 



I, 2. — SowERBY, Conch. Icon., XVI, 1866, pi. xliii, fig. 235. 

 Mya ventricosus Eaton, Zool. Text-Book, 1826, p. 221. 

 Margarita (Unio) ventricosus Lea, Syu., 1836, p. 23 ; 1838, p. 



18. 

 Margaron (Unio) ventricosus Lea, Syn., 1852, p. 26; 1870, 



p. 41. 

 Lampsilis ventricosus Baker, Moll, Chicago, Pt. i, 1898. p. 94, 



pi. XII, figs. 3-5. — Smith, Bull. U. S. Fish Com., 1899, p. 



291, pi. Lxxxiii. — Simpson, Syn., 1900, p. 526. 

 Lampsilis I'entricosa Stimson, Shells of N. Eng., 1851, p. 14. 

 Unio occidens Lea, Tr. Am. Phil. Soc, III, 1829, p. 435, pi. x, 



fig. 16; Obs., I, 1834, p. 49, pi. X, fig. 16. — KusTER, Conch. 



Cab. Unio, 1856, p. 170, pi. u, figs, i, 2. — Chenu, 111. Conch., 



1858, pi. XII, figs. 5, 5(X, 5^. 



