THE NATURAL HISTORY SURVEY. 103 
Distribution: “New York west to Nebraska, Michigan south 
to Texas and Georgia. 
Geological distribution: Pleistocene. 
Habitat: In lakes or rivers of considerable size, on a muddy 
bottom, in from five to twenty feet of water. 
Remarks: Avery distinct species, which can be confounded 
with no other; the females have the postero-ventral portion 
very much produced. It is one of the heaviest species we have. 
The nacre of the shell is the most beautiful of any of our species, 
varying from pure white to deep purple. It is confined to the 
southern and western regions. 
GROUP OF LAMPSILIS LUTEOLUS. 
32. Lampsilis luteolus Lamarck, pl. xi.; pl. xxvii., fig. 12. 
Unio luteolus Lam., Animaux sans Vertebres, Vol. VI., p. 79, 1818. 
Unio siliguotdeus BARNES, Amer. Jour. Sci. and Arts, Ist series, Vol. VI., 
p. 269, fig. 15, 1823. 
Unio inflatus BARNES, Amer, Jour. Sci. and Arts, Vol. VI., p. 266, 1823. 
Unio approximus Lea, Trans. Amer. Phil. Soc., Vol. X, p. 74, pl. v., fig. 
13, 1848. 
Unio afinis Lea, Trans. Amer. Phil. Soc., Vol. X., p. 271, pl. xix., fig. 26, 
1852. 
Unio distans ANTHONY, Amer. Journ. of Conch., Vol. I., p. 156, 1865. 
Shell; Large, elliptical, thin or very thick, more or less 
inflated, symmetrically rounded before and elongately oval be- 
hind, the female generally very obtuse; dorsal margin straight; 
ventral margin very slightly curved in the male and much pro- 
duced in the female; surface smooth and polished in some speci- 
mens, roughened by growth lines in others; umbones promi- 
nent, inflated, but not much elevated, brownish or greenish in 
color, generally eroded, and marked by about fourteen fine, un- 
dulating, elevated ridges, the apex directed anteriorly; ligament 
short, rather wide, stout, dark chestnut color; epidermis vary- 
ing from light, yellowish green to dark horn color or dark green, 
and generally with numerous dark green rays, which radiate 
from the umbones; the rays may be straight or crenulated and 
vary in width from 0.25 to 2.00 mill.; in old specimens the rays 
may be few in number, indistinct or wanting; anterior umbonal 
slope gracefully rounded, posterior long and flat, or slightly ex- 
cavated; cardinal teeth double in both valves; left anterior 
cardinal elevated, tooth-like, striated, right posterior long and 
narrow, not so much elevated, striated; right anterior cardinal 
very small, posterior large, elevated, pyramidal, coarsely striated 
