﻿l82 I.AMl'Sll.lS 



line. The female shell is a little fuller and more rounded on 

 the post-basal rej;ion, and sometimes has a well-developed 

 marsupial swelling. 



Length 138, height <So, diam. }^j mm. 



Entire ]Mississip])i River drainage; St. Lawrence system; 

 Red River of the Xorth ; Hudson River; eastern Texas. 



Type locality, Wisconsin River and "the lakes." 

 Unto gracilis Harni^s, Am. Jl. Sci., \J, 1823, p. 274. — Des- 



HAYHS, Tr. Element. Conch., 1839, p. 18, pi. xxx, figs. 2, 3. — 



Hanley, Biv. Shells, 1843, p. 174, pi. xx. fig. Z7- — ^es- 



HAYKS, Tr. Elem., IL 1853, p. 217. pi. xxx, figs. 2, 3. — Sow- 



ERBY, Conch. Icon., XVI, 1866, pi. xxxix, fig. 215. 

 Mya gracilis Eaton, Zool. Text-Book, 1826, p. 222. 

 Symphynota gracilis Lea, Tr. Am. Phil. Soc, III, 1830, p. 452; 



Obs., I, 1834, p. 66. 

 Margarita (Unio) gracilis Lea, Syn., 1836, p. 11 ; 1838, p. 13. 

 Metaptera gracilis Stimpson, Shells of N. Eng., 1851, p. 14. 

 Margaron (Unio) gracilis Lea, Syn., 1852, p. 19; 1870, p. 28. 

 ? Alio don gracilis Sowicrp.v, Sowerby's Genera, No. XVII, 



1823, fig. 

 Lampsilis gracilis Baker, Moll. Chicago, Pt. I, 1898, p. 99, pi. 



XIX, fig. I. — Simpson, Syn., 1900, p. 573. 

 Paraptera gracilis Ortmann, Ann. Car. Mus.. VIII, 1912, p. 



331- 



Unio frogilis Svvainson, Zool. Ill, ist sen. III, pi. CLXXi, 



1823. CONKAD, Monog., VI, 1836, p. 55, pi. XXX. — KUSTER, 



Conch. Cab. Unio, 1852, p. 19, pi. in, fig. i. 

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

 Metaptera fragilis Conrad, Pr.Ac. N. Sci. Phila., VI, 1853, 



p. 260. 

 Unio fragilis var. gracilis P.iJTEL, Conch. Sam., Ill, 1890, p. 



153- 

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



Unio planus Conrad, New F. W. Shells, 1834, p. 71. 



Unio (Niaa) atrata Swainson, Zool. 111., 1841, pi. clxxi. 



Unio atratus Hanley, Test. Moll, 1842, p. 199; Biv. Shells, 



1843, P- 199' pl- ^^f' fif?. 29. 



