THE NATURAL HISTORY SURVEY, 71 
for nearly the whole length of the posterior margin; liver dark 
brown. Pulsations of the heart regular, twenty per minute. 
Another animal examined had but fourteen heart pulsations. 
Distribution: ‘Western New York to Minnesota and Kan- 
sas; south to Texas and east to Georgia. (Call. ) 
Geological distribution: Pleistocene. 
Habitat: In muddy rivers, in from ten to fifteen feet of 
water. 
Remarks: A common and widely distributed species, 
recognized by its dull brown shell. It varies greatly in its 
length, some specimens being short and stumpy, and others 
long and narrow, in this form much resembling ZLampsilis rectus. 
The umbonal sculpture is very pronounced, and helps notalittle 
to distinguish the species. In some specimens there are faint 
indications of dark rays, but the typical form is entirely rayless. 
The nacre varies from pinkish white to very deep purple, andin 
this state very much resembles Lampszlis rectus. It is widely 
distributed, being found in the northern, western and southern 
regions. 
GROUP OF UNIO HILDRETHIANUS. 
12. Unio hildrethianus Lea’, pl. v., fig. 4. 
Margaritana hildrethiana Lea, Journ. Acad. Nat. Sci., Phil., Vol. IV., p. 
49. * 
Shell: Small, long, compressed, thin, rounded before 
and broadly rounded behind; dorsal and ventral margins 
straight; surface smooth, the growth lines distinct and consider- 
ably elevated on the anterior parts; umbones small, prominent 
but not much elevated, dark brown in color and marked by three 
or four elevated wrinkles arranged in a double loop; ligament 
rather short and narrow, light horn color; epidermis yellowish, 
greenish or brownish, sometimes streaked with reddish brown, 
perfectly plain; cardinal teeth very small, thick, depressed; 
lateral teeth barely indicated by a thickening of the hinge line; 
muscle scars very broad, scarcely impressed, lightly striated; 
dorsal muscle scars very small, deep; pallial linea trifle im- 
pressed; cavity of the beaks very shallow; nacre bluish with a 
white patch on the anterior part, iridescent. There is a pecu- 
liar “bulge”? extending from the umbones diagonally to the 
postero-ventral border. 
Length, 41.50; height, 19.50; breadth, 12.50 mill. (12949). © 
88.00; “ 18.00; ‘ 11.00 " (12049). g 
*Mr. Simpson states that the generic position of this species is doubtful, and that it may 
take generic rank by itself; Mr. Simpson has been unable, as has alsothe author, to find 
specimens in a perfectly gravid condition. 
