﻿r,AMPSILI-S 189 



upper Mississippi River drainage, south to the Tennessee 

 River ; Buffalo, New York ; southern Michigan ; Souris River, 

 Manitoba. 



Type locaHty, lower Ohio River. 

 Unio (Leptodea) leptodon Rapinesquk, Ann. Gen. Sci. Phys. 



Brux., V, 1820, p. 295, pi. Lxxx, figs. 5-7. 

 Unio leptodon Say, Am. Conch., VI, 1834. — Conrad, Monog., 



VII, 1836, p. 58, pi. xxxiii. — Chrnu, Bib. Conch., ist sen, 



III, 1845, P- 12, pi. I, figs. 5-7. — KuSTRK, Conch. Cab. Unio, 



1861, p. 197, pi. Lxiv, figs. I, 2. — SowERLJY, Conch. Icon., 



XVI, 1866, pi. XLViii, fig. 257. 

 Symphynota leptodon Ferussac, Guer. Mag., 1835, p. 25. 

 Leptodea leptodon Conrad, Pr. Ac. N. Sci. Phila, VI, 1853, 



p. 262. 

 I.ampsilis leptodon Simpson, Syn., 1900, p. 575. 

 Anodon piirparascens Swainson, Zool. 111., ist sen. III, pi. 



CLX, 1823. 



Unio velum Say, New Harm. Disseminator, II, September 27), 



1829, p. 293. 

 Symphynota tcnuissiiua Lea, Tr. Am. Phil. Soc, III, 1829, p. 



453. pl- -^i. fig- 21 ; Obs., I, 1834, p. 67, pi. xi, fig. 2n 

 Margarita (Unio) tenuissimus Lea, Syn., 1836, p. 38; 1838, 



P- 25. 

 Unio tenuissimus Hanley, Biv. Shells, 1843, P- 206, pi. xx, 



fig. 42. — SowERBY, Conch. Icon., XVI, 1866, pi. xLiv, fig. 



240. 

 Margaron (Unio) tenuissiinns Lea, Syn.. 1852, p. 38; 1870, 



p. 61. 



A peculiar shell of irregular growth. When viewed from 

 above or below it will be seen that the parting line between 

 the valves is never straight, the shell being more or less twisted 

 to the left or the right or both ways as in the genus Pseudo- 

 spatha. The anterior and posterior openings are very uneven 

 and quite large. The teeth are rudimentary and in some speci- 

 mens almost entirely wanting. 



