772 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XXII. 



(Group of Qiiadnila trupczoiHeH.) 



Shell rhomboid, 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 

 papilla' or crenulations. 



tQUADRULA TRAPEZOIDES Lea. 1 



* Unio erassidens vir. a, LAMARCK, An. sans Vert., VI, 1819, p. 71. 3 

 *Plectonwu8 crassidena var. a, CONRAD, Pr. Ac. N. Sci. Phila., VI, 1853, p. 261. 



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



1834, p. 79, pi. in, fig. 1.* CONRAD, New F. W. Shells, 1834, p. 72 * FER- 

 USSAC, Guer. Mag., 1835, p. 27. *HANLEY, Test. Moll., 1842, p. 176; *Biv. 

 Shells, 1843, p. 176, pi. xxn, fig. 29. * CATLOW and REEVE, Conch. Norn., 

 1845, p. 64. *H. and A. ADAMS, Gen. Rec. Moll., II, 1857, p. 497. * CHENU, 

 111. Conch., 1858, pi. x, figs. 2, 2a, 26; Manual, 1859, II, p. 142, fig. 699. 

 *KUSTER, Conch. Cab., 1862, p. 274, pi. xcn, fig. 2. * REEVE, Conch. Icon., 

 XVI, 1864, pi. v, fig. 17. *B. H. WRIGHT, Check List, 1888. * PyETEL 

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



"Marf/arita (Unio) trapezoides LEA, Syn., 1836; p. 12; 1838, p. 14. 



*Margaron (Unio) trapezoides LEA, Syn., 1852, p. 21; 1870, p. 31. 



Unio intemiptus SAY, Transylvania Journal, IV, 1831, p. 525; * Ana. Conch., IV, 

 1832, pi. xxxni, VI, 1834.* FERUSSAC, Guer. Mag., 1835, p. 28.* DESHAYES, 

 An. sans. Vert., 2d ed., VI, 1835, p. 556; 3d ed., II, 1839, p. 675. *TROSCHEL, 

 Arch, fur Naturg., V, 1839, Pt. 2, p. 234. * CHENU, Bib. Conch., 1st ser., Ill, 

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



* Unio dombeyana VALENCIENNES, Rec. Obs. Zool., II, 1833, p. 227, pi. LIII, figs. 



1, la, Ifc. 



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

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

 west Tennessee. 



'In 1820 Rafinesquo 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 I'layiola of 

 the genus Obliquaria and not in Unio at all, it does not have priority in the latter 

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

 vania Journal the species which Dr. Lea called Unio trapezoides as Unio inierruptus. 

 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 trapezoides Lea according to Lea, who examined tho Lainarckian 

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



