THE NATURAL HISTORY SURVEY. 77 
larger, ashy salmon, free from the abdominal sac; all four gills 
moderately filled with embryos throughout. (Simpson.) 
Distribution: ‘Western New York to Minnesota, and 
Iowa, and Kansas;to Texas, east to Mississippi and Ten- 
nessee.”’ (Call.) 
Geological distribution: Pleistocene. 
Habitat: In the larger rivers, on a muddy bottom, in 
rather deep water. 
Remarks: A very distinct species, at once recognized by 
its heavy trigonal form, elevated umbones and cordate appear- 
ance when viewed anteriorly. Specimens have been found 
fossil on an old lake beach, now half a mile from the lake, while 
digging foundations for new buildings. They were found at a 
depth of from five to ten feet below the surface. One specimen 
found while digging a cellar on Hall Street seems to be inter- 
mediate between /rigona and rudiginosa; it has the length and 
height of rudigimosa and the trigonal and inflated shape of 
trigona. The cardinal teeth are more elevated and deeply 
sulcated in some specimens than in others, and some forms are 
longer in proportion to their height. So far as known it is 
found only in the Calumet River, in which stream Messrs. T. 
Jensen and H. B. Derr found each a single dead specimen. The 
individual collected by Mr. Derr seems to be a cross between 
rubiginosa and ¢rigona, having the length and general shape of 
the former and the inflated and elevated umbones of the latter. 
16. Quadrula rubiginosa Lea, pl. xix., fig. 2; pl. xx., fig. 1. 
Unio rubiginosus Lea, Trans. Amer. Phil. Soc., Vol. III., p. 409, pl. 
viii., fig. 10, 1829. 
Unio flavus RAFINESQUE, Conrad in monograph, p. 74, pl. xli., fig. 2, 
1837. 
Shell; Elliptical or quadrate, rather thick, compressed, 
sometimes constricted in the center of the shell, incrassate, 
rounded before, squarely truncated behind; dorsal border 
slightly curved; ventral border straight or curved; surface 
roughened by lines of growth, which are elevated into sharp 
ridges; umbones a trifle elevated, inflated, light yellowish 
brown, marked by five or six heavy, elevated, rounded ridges; 
anterior umbonal slope rounded; posterior slope angulated, 
excavated in some specimens; ligament short, wide, solid, very 
dark brown; epidermis dark horn colored or yellowish, darker 
in old specimens, and with very faint indications of rays in 
young specimens; cardinal teeth double in both valves, about 
