OF DENISON UNIVERSITY. 
37 
vex throughout, not affected by a sinus medianly as usual in the genus; 
hinge-line shorter than the shell ; posterior side slightly oblique form- 
ing an angle of about ioo° with the hinge; anterior margin apparent- 
ly meeting the hinge at nearly a right angle ; surface depressed poster- 
iorly but elsewhere gently and nearly uniformly convex, marked by 
both radiating and concentric striae, the former consisting of minute 
wavy lines on the post-umbonal space, four or five strong costae on the 
umbonal prominence and passing to the postero-inferior angle, and 
very fine, straight, close radii on the remainder of the shell, the whole 
being delicately and finely cancellated by concentric striae. 
Perhaps this species most nearly resembles M. tenuistriata of the 
coal-measures, from which it differs in lacking the sinus below, in the 
surface markings and outline. 
A similar but smaller form is figured by Hall from Bedford, O. , 
but seems to agree with M. hamiltoniae in markings. 
M. chemungensis possesses the sinus and differs in markings. The 
resemblance to M. micronema, M. and W. * is much more striking 
apparently, but our shell is larger and less extended. Length 33 mm. 
height 17 mm. Length of another specimen 41 mm. 
Near Newark, O., about 60 or 70 feet above congl. II in our di- 
vision III. 
MACRODON STRIATO-COSTATUS, sp. u. 
(Plate VI, Fig. 7 ; Plate XI, Fig. 37.) 
Cf. Macordon pai'vus^ W. and W.] 
A small Macrodon of the same group as M. newarkensis is found 
in shales seventy feet below conglomerate I, in Ashland Co. It is, 
however, a smaller species and does not have the enlarged striae, on 
the post-umbonal ridge. 
Shell small, transversely semi-elliptical, a little broadest posterior- 
ly, hinge nearly equalling the greatest length ; beak about one-fourth 
from the front, somewhat prominent ; anterior outline a gentle curve, 
beginning at the hinge with a little more than a right angle, it curves 
more rapidly as it enters the ventral margin which is more or less con- 
vex ; posterior outline somewhat concave ; surface convex about the 
umbonal region, quite flat posteriorly, marked by strong concentric 
•I'Proc. Acad. Nat. Sci. Phila. 1886, p. 261, 
