26 
BULLETIN OF THE LABORATORIES 
iired IS elongate, almost linguliform; beak acute, prominent; hinge line 
less than yi the height of the valve, which is strongly convex near the 
median line and ornamented with fine radiating and concentric striae. 
Aviculopecten coxanus, M. and W. 
(Plate I, Figs. 4 and 17.) 
This little shell is not uncommon at Flint Ridge- and Bald Hill, 
and curiously enough is generally preserved so as to expose the inte- 
riors, this fact led to some confusion, as the shell is so thin that the 
markings involves the whole shell and the inside is therefore a nega- 
tive copy of the outer surface. Our largest specimen is of the size of 
the specimen figured by Meek, but presents the inner surface. This 
species maybe recognized by the slight obliquity (more than indicated 
by Meek) and alternating striae. The striae seem to be uniformly more 
prominent than in the type, the striae are also square in section. The 
posterior ear is acute with its posterior outline concave, less distinctly 
separated from the valve than the anterior ear, which is less acute. 
Length, .50; width, .49; hinge line, .40. About 14 primary striae on 
the body of a valve of this size with alternating minute ones. 
Aviculopecten scalaris, sp. n. ? 
(Plate I, Fig. 8.) 
We have been tempted to regard this as a form of A. occidehtalis, 
but there is a marked dissimilarity in the markings. The shell is 
equivalve, the valves nearly alike; somewhat longer than wide; hinge 
line shorter than greatest width ; lower margin a uniform curve ; front 
margin strongly curved, anterior ear separated from the body of the 
shell by a sharp depression ; posterior ear larger, more excavated on 
its lateral margin and less distinctly marked off from the valve. The 
valves are marked by fascicles of triangular, prominent striae or ridges, 
which increase by bifurcation, usually with a feeble preference for 
dichotomy; these ridges crossed by sharply marked concentric angu- 
lar depressions causing a resemblance to the treads of a stairway ; also 
concentric lines most prominent upon the ears. The coarser wrinkles 
might have been thought accidental, but for the constancy with which 
they appear. After making the corrections indicated by Meek (Geo- 
