QUADRULA 815 
valve with three pseudocardinals, the middle one large and 
frequently much split, with one lateral, which is sometimes 
partly double; beak cavities deep, compressed; muscle scars 
shallow, the anterior very rough; nacre white, much thinner 
and iridescent behind; pallial line strongly crenate. 
Length 1109, height 83, diam. 54 mm. 
length 120, height 90, diam. 46 mm. 
Length 90, height 62, diam. 52 mm. 
Upper Mississippi drainage area south to the Tennessee and 
Arkansas rivers; Red River of the North; Saskatchewan Riv- 
er; Lake Winnipeg; western Michigan. 
Type locality, Lake Erie. 
Unio plicata Say, Nich. Encyc., II, 1817. 
Unio (Theliderma) plicata Swatnson, Tr. on Mal., 1840, p. 
271, fig. 54e. 
Mya plicata Eaton, Zool. Text-Book, 1826, p. 219. 
Ouadrula plicata BAKER, Moll. Chicago, Pt. 1, 1898, pl. xxv, 
fig. I.—SIMPSON, Syn., 1900, p. 767. 
Unio plicatus HAntEy, Biv. Shells, 1843, p. 175, pl. xx1, fig. 
21.—KustER, Conch. Cab. Unio, 1856, p. 137, pl. XL, fig. 3. 
—Rerrve, Conch. Icon., XVI, 1864, pl. 11, fig. 5. 
Margarita (Unio) plicatus Lea, Syn., 1836, p. 12; 1838, p. 14. 
Margaroen (Unio) plicatus Lea, Syn., 1852, p. 20; 1870, p. 30. 
Plectomerus plicatus Conran, Pr. Ac. N. Sci. Phila., VI, 1853, 
p. 261. 
Unio peruziana L,AMARCK, An. sans Vert., VI, 1819, p. 71.— 
Drsuayrs, Encyc. Meth., 1827, pl. 248, fig. 7; pl. 249, fig. 1. 
Unio crassus BARNES, Am. Jl. Sci., VI, 1823, p. 118. 
Unio rariplicata DesHayes, Enc. Mth., II, 1830, p. 578. 
Unio giganteus Lea, Obs., II, 1838, p. 35. 
Unio heros Kuster, Conch. Cab. Unio, 1856, p. 136, pl. Xt, 
Bes. Te 2. 
An exceedingly variable species in general form, degree of 
inflation. development of beaks, etc. As in most of the species 
of this group there are occasional specimens that are wholly 
destitute of plications. Normally it is perfectly distinct from 
its near ally Ouadrula undulata, being more inflated, solider 
