QUADRULA 831 
Streams flowing into the Gulf of Mexico, from the Alabama 
River west to eastern Texas; northward in the Mississippi 
system to northwest Tennessee. 
Type locality, Lake St. Joseph. La. 
Unio crassidens var. a, LAMARCK, An. sans Vert., VI, 1819, 
pazie 
Plectomerus crassidens var. a, CONRAD, Pr. Ac. N. Sci. Phila., 
VI, 1853, p. 261. 
Unio trapesoides Lea, Tr. Am. Phil. Soc., IV, 1831, p. 69, pl. 
1, fig. 1; Obs., I, 1834, p. 70, pl. 1m, fig. 1—Hantey, Biv. 
Shells, 1843, p. 176, pl. xx11, fig. 29.—CHENU, Ill. Conch., 
1858, pl. x, figs. 2, 2a, 2b; Manual, 1859, II, p. 142, fig. 690. 
—Kuster, Conch. Cab., 1862, p. 274, pl. xct1, fig. 2—REEVE. 
Conch. Icon., XVI, 1864, pl. v, fig. 17. 
Margarita (Unio) trapezoides Lea, Syn., 1836, p. 12; 1838, 
pi 34. 
Margaron (Unio) trapezoides Lea, Syn., 1852, p. 21; 1870, 
Piost: 
Quadrula trapezoides SIMPSON, Syn., 1900, p. 772. 
Crenodonta trapezoides ORTMANN, Ann. Car. Mus., VIII, 
1912, p. 248, figs. 5-5a. 
Unio interruptus Say, Transylvania Journal, IV, 1831, p. 525; 
Am. Conch., IV, 1832, pl. xxx111.—CHENU, Bib. Conch., 1st 
ser., ITI, 1845, p. 45, pl. xvu, figs. 1-3. 
Unio dombeyana VALENCIENNES, Rec. Obs. Zool., II, 1833, p. 
227, Ol. El. eS. IY. 1d, 10: 
Ouadrula heros dombeyana Vanatra, Naut., XXIII, 1910, 
Pp. FO2: 
The only number of the section with purple, red or coppery 
nacre. 
Var. pentagonoides FRIERSON. 
“This shell differs from the type in having its dorsum very 
much arched or bent midway. The posterior is widely bian- 
gulated. The anterior is singularly truncated like U. corus- 
cus Gld. The effect being that the outline forms nearly an 
equilateral pentagon, hence the name. Aside from its form, 
