80 THE CHICAGO ACADEMY OF SCIENCES. 
white about the adductor muscles anda part of the foot and 
abdomen, which latter is yellowish; ctenidia short and wide, 
rounded before and behind, united above and to the opposite 
pair throughout their entire length; labial palpi triangular, yel- 
lowish at base and bluish white at tip, united at base and partly 
on the posterior side; foot large, flesh colored; siphonal open- 
ings yellowish inside shading to brownish; anal opening slightly 
crenulated, small; branchial with numerous brownish or blackish 
papille; edge of mantle black; liver dark brown. Four gills 
used as marsupia. 
Distribution: Mississippi and Ohio valleys. 
Geological distribution: Pleistocene. 
Flabitat: In rivers, in soft, black mud. 
Remarks: This species is closely related to Q. rwbiginosa, 
but may be distinguished by its inflated umbones, roundly 
elliptical shell, produced postero-ventral margin and its heavy 
cardinal teeth. In some specimens the pink nacre serves asa 
distinguishing character, but only about thirty per cent are thus 
colored, the others having awhite nacre. The young more nearly 
resemble rudiginosa, but as they beome older the characters of 
coccinea become more pronounced. In the DuPage River a 
form is sparingly found, which Prof. R. E. Call says is a cross 
between this species and either ¢vigona or rubiginosa. As rubig- 
inosa is the only other form of this group found in the DuPage 
River, the cross must be between these two species. The cross 
has a thicker and more quadrate shell than the typical form. 
This is a very significant fact, which may account for much of 
the perplexity attending the identification of the Unionide. The 
species seems to be confined to the Desplaines River drainage. 
GROUP OF QUADRULA PLICATA. 
18. Quadrula plicata Lesueur, pl. xxvi., fig. 1. 
Unio plicatus Lesuzur, Lea, Trans. Amer. Phil. Soc., Vol. III., p. 409, 
1829. 
Unio rariplicata LaMaRck, Animaux sans vertebres, ed. 1818, Vol. VI., p. 
Wale 
Unio hippopaeus Lea, Trans. Amer. Phil. Soc., 2d series, Vol. X., p 67, pl. 
i., fig. 1, 1845. 
Shell: Broadly elliptical, plicate, very thick and solid, 
inflated, rounded before and quadrate behind; dorsal and 
ventral borders almost straight; surface heavily marked by 
growth lines and by from four to six rather heavy plications 
which extend in a diagonal direction across the shell, passing 
