36 
BULLETIN OF THE LABORATORIES. 
the hinge ; rather gibbous, usually with a broad impression extending 
from the beaks obliquely backward and downward to the middle of 
the base of each valve ; anterior side extremely short, or nearly obso- 
lete, convex, and rounded; posterior side broader, more compressed 
or cuneate, with its upper edge straight and sloping obliquely back- 
ward to the regularly rounded posterior margin ; base broadly and 
slightly sinuous in the middle, and rounding upward at the extremities; 
hinge line straight, between one-half and two-thirds as long as the 
valves, ranging at an angle of about 25 deg. with the oblique, longer 
axis of the shell, so as to meet the sloping upper edge of the posterior 
margin at a very obtuse but moderately well-defined angle, this im- 
parting to the somewhat compressed posterior dorsal region a very 
faintly alate appearance ; beaks extremely oblique, depressed nearly 
to the dorsal margin, very nearly terminal, and scarcely projecting be- 
yond the rounded outline of the anterior extremity. Surface orna- 
mented by fifteen to twenty exceedingly regular, well-defined, sub-im- 
bricating, flattened ridges or undulations, that gradually become small- 
er and more closely approximating on the umbones. Length of larg- 
est specimen seen 0.55; height at the posterior extremity of 
hinges -32.” 
The specimen figured is but 0.45 long, but agrees well with the 
description, it being a partial cast, shovVing hinge teeth distinctly. 
Gervillia i?) ohioense, sp. n. 
(Plate IV, Fig. 13, and Plate III, Fig. 12.) 
(Cf. Avicitla lon^a, Meek. 
Two specimens have been secured from Flint Ridge, both some- 
what imperfect, but indicating a species quite different from Monop- 
teria gibbosa. The whole question of the generic affinity of the car- 
boniferous species referred to Gervillia, Monopteria, Blakevellia, etc., 
is very obscure. 
The upper outline is nearly straight ; beak distant nearly one-third 
''the length from the anterior margin; posterior wing greatly produced, 
• posterior margin deeply sinuous ; posterior, produced part of shell 
■ keeled ; anterior wing acute, its margin very oblique and slightly curved 
to its junction with the lower margin, with which it forms a continuous 
symmetrical curve. Hinge line, .65, height, .45, greatest length, .85. 
