136 THE NAUTILUS.
being less elongated and more inflated with more prominent beaks.
The color both of the epidermis and nacre is also quite different.
Messrs. Frierson and Marsh, to whom specimens have been sub-
mitted, agree that it is distinct from any described fo:m, and Mr.
Simpson remarks that it <k looks more or less like two or three species,
but I cannot refer it to anything." Mr, B. H. Wright suggests that
it is close to some forms of U. confertus Lea, but both in shape and
color, which is remarkably constant in all the specimens seen, it
seems sufficiently distinct.
UNIONIDAE FROM MOCCASIN CREEK, A TRIBUTARY OF THE
Lampsilis anodontoides floridensis Lea.
" lienosus Con. (caliyinosus Lea).
" vibex Con. (i-utilans Lea) v
Unio' downiei Lea, var.
arctatus tortivus Lea.
A very large, heavy, inflated form similar to Lea's tetricus, longer
but not so swollen as that figured by Simpson in Proc. U. S. Nat.
Mus. xv. PI. Ixiv. figs. 3 and 4. Associated with this form is an-
other more compressed, strongly rayed and with umbonal slope,
decidedly biangulate, which Mr. Simpson thinks is also referable
here. Mr. Marsh considers this identical with Wright's nolani, a
synonym of the following species.
Unio obnubilis Lea. Two specimens smaller, thicker and appar-
ently quite distinct from the last-mentioned form are referred to
santeensis Lea, by Marsh, to which Simpson somewhat doubtfully
A NEW SPECIES OF MEDIONIDUS.
BY BRYANT AVALKER.
Medionidus sirupsonianus n. sp. PI. ix. figs. 4 and 5.
Shell small, rather thin, somewhat inflated, elliptical, inequilateral,
strongly plicate on the posterior slope. Epidermis dark yellow,
smooth, polished, covered with dark green pencilled rays which tend
to break into a net-work of angular lines covering the entire surface.
Anterior end compressed, rounded, and slightly elevated above the