298 
Aug. F. Foerste 
31. Ischyrodonta curta, Conrad 
{Anadontopsis unionoides, Meek, Pal. Ohio, vol. I, pi. XII, Fig. 2) 
{Plate III, Figs. 14 A, B) 
In the exposures at Bennett^s bridge, a mile down stream from 
Salmon River Falls, a species is quite common which can not be 
distinguished from Ischyrodonta unionoides, from the Fairmount 
member of the Maysville division of the Cincinnatian. What 
must be called the basal margin is slightly less convex, so that 
the angle with the cardinal margin becomes more acute, and the 
curvature at the anterior margin correspondingly greater. More- 
over, the cardinal margin posterior to the beak is straighter, for a 
distance about as far as the anterior margin extends forward from 
the beak; in consequence, the angle between the cardinal margin 
and the posterior is slightly more angular. The oblique lines 
being accentuated, the shell is slightly less rotund, but the differ- 
ences are scarcely specific. 
The species also occurs at lower horizons, being found within a 
hundred yards down stream from the railroad bridge, east of 
Pulaski. At the higher horizon, it occurs also two and a half 
miles east of Worth ville. A similar form occurs two miles west 
of Worth ville. 
This shell is so common at some of the upper horizons in the 
Lorraine, that it could hardly have escaped the attention of the 
early investigators. It is identical with the Cypricardites curta of 
Conrad, described from a corresponding horizon. The following 
is the original description, published in the fifth annual volume 
of the New York Geological Survey, on p. 53, in 1841. 
Suborbicular, compressed; hinge margin elevated; posterior margin 
obtusely rounded. Localities. Near Rome, Oneida county, Richmond, 
Indiana. 
It is the only shell at the Talcott and Comstock quarries, 
two miles south of Rome, which could be described as subor- 
bicular. The specimen of Ischyrodonta curta figured by Hall 
{Paleontology of New York, vol. I, plate 81) from Grimsby, in 
Canada, is a very typical form of the species. Fig. 2a, on plate 
82, however, which may be regarded as the type of Hall’s spe- 
cies, Modiolopsis curta, is a small individual of Pterinea demissa. 
