ae N Serius. 
VOL. VII. MAY, 1898. No. 1 
ILLUSTRATIONS OF NEW SHELLS.! 
Unio Pilsbryi Marsh, Plate I, figs. 7, 8. 
This species is a member of the plicate group of Uniones. It is 
a decidedly compressed, oblong shell, black in color, having very 
distinctly marked lines of growth, which are spaced over the greater 
part of the disk, but become crowded on the lower margin. It has 
numerous oblique waves, which generally bifurcate indistinctly 
toward the posterior-lower end. The waves are more or less cut by 
short impressed furrows, asin U. undulatus, ete. The nacre is white 
and very thick anteriorly, but in the cavity of the valves and pos- 
teriorly it is thin and stained with blue and olive-green. The lat- 
eral teeth are also olive-green. 
It was collected by Mr. Elwood Pleas in the Little Red River, 
Arkansas, and the original description, by Mr. Wm. A. Marsh, will 
be found in the Nautitus, V, p. 1. 
Unio Pilsbryi is not closely allied to any other American species. 
It has a striking resemblance to Unio Leai Gray of China. 
Specimens, including the individual figured, are in the special 
exhibit of United States shells, formed by the American Association 
of Conchologists, in the Museum of the Academy of Natural 
Sciences of Philadelphia. 
1The accompanying plate is reprinted by permission from the Proc. Acad. 
Nat. Sci. of Philadelphia. 
