THE NATURAL HISTORY SURVEY. 97 
Remarks: A species at once distinguished by its subovate 
outline, inflated beaks and numerous rays, which radiate from 
the umbones to the ventral and lateral margins. The umbonal 
markings are very distinct and peculiar, and the wavy character 
of the rays is not found in any other species which inhabit this 
area. It seems to be confined to the lakes in the southern 
region. 
Section METAPTERA Rafinesque. 
GROUP OF LAMPSILIS ALATUS. 
28. Lampsilis alatus Say, pl. xviii. 
Unio alatus Say, Nich. Encyc. Vol. IV., fig. 2 2, 1816. 
Shell; Large, rather solid, symphynote, broadly oval in out- 
line in old specimens but obtusely triangular in strongly alate 
forms, somewhat inflated when adult but compressed when 
young, rounded before and generally very broadly rounded be- 
hind, although some specimens are triangulate; umbonal slopes 
rounded; the alate postero-dorsal margin is very much com- 
pressed, and when perfect is exactly triangular in shape, ex- 
tending from the umbones to the posterior end of the shell; in 
old specimens, or those in which the “wing”’ is not fully de- 
veloped, the shapeis not soclearly defined; ventral margin slightly 
rounded; surface smooth and shining on the central part of the 
shell, with the lines of growth large and coarse on the anterior, 
posterior and ventral margins and the alate portions; epidermis 
black or greenish black, in the young yellowish horn, perfectly 
plain and rayless in old specimens but distinctly rayed with 
numerous fine green rays over a yellowish background in young 
and half grown specimens; umbones depressed, flush with the 
hinge line, ornamented by several very fine raised ridges; liga- 
ment large, solid, light brown in color; cardinal teeth double in 
both valves, those in the left valve about equal in size, long and 
narrow, elevated, strongly grooved on their anterior faces; those 
in the right valve unequal in size, the anterior tooth small, the 
posterior tooth large and similar in form to those of the left 
valve; lateral teeth long, thin, lamellar, elevated, very slightly 
arcuate, smooth; anterior adductor muscle scar deeply im- 
pressed, striated; posterior adductor muscle scar large, very in- 
distinct, confluent; pro/ractor pedis muscle scar deeply impressed, 
striated; pallial line distinct, impressed, somewhat crenulated; 
dorsal muscle scars in the cavity of the beaks and arranged in 
nearly a straight row, deeply pitted; there are from six to seven 
