772 PEOCEEDINGS OF THE NATIONAL MUSEUM. vol.xxii. 



(Group of Quadrula trapezoides.) 



Shell rlioinboid, inflated, with a high posterior ridge; beak sculpture 

 coarse, irregular corrugations swollen to nodules on the posterior ridge; 

 surface sculptured on posterior half with oblique ridges, which are 

 sometimes corrugated, and with strong corrugations on post slope beak 

 cavities only moderately deep ; nacre purple. 



Animal with the gills slightly rounded below, inner the larger 

 throughout, free from the abdominal sac; palpi enormous, long; 

 branchial opening very large, finely papillose; anal opening with fine 

 papilLb or crenulations. 



I QUADRULA TRAPEZOIDES Lea.i 



* Unio crassidens var. a, Lamakck, An. sans Vert., VI, 1819, p. 71.^ 



^Plectomeriis crassidens var. a, Conkad, Pr. Ac. N. Sci. Phila., VI, 18.53, p. 261. 



"Unio trapezoides Lea, Tr. Am. Phil. Soc, IV, 1831, p. 69, pi. in, fig. 1; " Obs., I, 

 1834, p. 79, pi. Ill, fig. 1.—* Conrad, New F. W. Shells, 1834, p. 72 — * Fer- 

 USSAC, Guer. Mag., 1835, p. 27.— "Hanlky, Test. Moll., 1842, p. 176; * Biv. 

 Shells, 1843, p. 176, pi. xxii, fig. 29. — * Catlow and Reeve, Conch. Nom., 

 1845, p. 64.— *H. and A. Adams, Gen. Rec. Moll., II, 1857, p. 497.—^ Chenu, 

 111. Conch., 1858, pi. x, figs. 2, 2a, 2b; Manual, 1859, II, p. 142, fig. 699.— 

 * KusTER, Conch. Cab., 1862, p. 274, pi. xcii, fig. 2. — * Reeve, Conch. Icon., 

 XVI, 1864, pi. V, fig. 17.— *B. H. Wright, Check List, 1888.— * Pjetel 

 Conch. Sam., Ill, 1890, p. 169. 



^Margarita (Unio) trapesoides Lea, Syn., 1836; p. 12; 1838, p. 14. 



^Margaron ( Unio) trapesoides Lea, Syn., 1852, p. 21; 1870, p. 31. 



Unio interruptus Say, Transylvania Journal, IV, 1831, p. 525; *Am. Couch., IV, 

 1832, pi. XXXIII, VI, 1834.—* Ferussac, Guer. Mag., 1835, p. 28.—* Desha yes, 

 An. sans. Vert., 2d ed., VI, 1835, p. 556; 3d ed., II, 1839, p. 675.— ^Troschel, 

 Arch, fiir Naturg., V, 1839, Pt. 2, p. 234.— * Chenu, Bib. Conch., 1st ser.. Ill, 

 1845, p. 45, pi. XVII, figs. 1-3. 



""Unio domheyava Valenciennes, Rec. Obs. ZooL, II, 1833, p. 227, pi. liii, figs. 

 1, la, Ih. 



Streams flowing into the Gulf of Mexico, from the Alabama Eiver 

 west to eastern Texas; northward in the Mississippi system to north- 

 west Tennessee. 



^ In 1820 Rafinesque applied the name interrupta to some, to me, unknown Unio, in 

 Ann. Gen. Sci. Phys. Brux., but as he placed his species in the subgenus Plagiola of 

 the genus Obliquaria and not in Unio at all, it does not haA^e priority in the latter 

 genus. In 1831 (December, according to Dr. Lea) Say described in the Transyl- 

 vania Jourual the species which Dr. Lea called Unio trapezoides as Unio interruptus. 

 In the latter part of the same year (I am unable to ascertain the exact date) Dr. Lea 

 published his name in the Transactions of the American Philosophical Society. As 

 I have found it impossible to determine which name was actually published first I 

 have used the better known — that of Dr. Lea. 



2 This is Unio trapesoides Lea according to Lea, who examined the Lamarckian 

 types. See Synopsis, 4th ed., p. 37, footnote. 



