Notes on Cincinnatian Fossil Types 
335 
also the number 407 which it had in the Faber collection. It was 
obtained at Versailles, Indiana, presumably in the Waynesville 
division of the Richmond. The shell unquestionably belongs to 
the Pholadomorpha pholadiformis group, and, if it differs at all from 
the latter species, this difference consists chiefly in a smaller devia- 
tion between the cardinal and basal margins. However, there is a 
probability that in a perfect condition of the shell the cardinal margin 
would be straighter for a longer distance posteriorly, and that the 
basal margin would deviate more from the cardinal margin. Ac- 
cepting this interpretation, the type of Modiolopsis capax is less 
interesting as a possible new species than as an excellent representa- 
tive of an old one. 
Most specimens of Pholadomorpha pholadiformis preserve the 
valves in a more or less compressed condition, owing to their pres- 
ervation chiefly in clay shales or in very argillaceous limestones. 
The type of Pholadomorpha capax, however, is preserved in a fine 
grained limestone, and, apparently, retains its original convexity 
very well, as far as it is preserved at all. From this the following 
description is drawn. 
The greatest thickness of the shell, or distance between the 
valves, occurs at mid-length, along the umbonal ridges. From this 
point the shell tapers both anteriorly and posteriorly. The thickest 
part of the shell is about 20 millimeters posterior to the beak, where 
it equals 20 millimeters. At the beaks, the thickness is reduced 
to about 14 millimeters. Forty millimeters posterior to the beak, 
the thickness still equals 19 millimeters, but posterior to the latter 
point the reduction in thickness is more rapid. 
The umbones are strongly compressed and flattened, the flatten- 
ing affecting practically all of the shell anterior so the umbonal 
ridge. Basal margin straight, mesial sulcus practically obsolete. 
Umbonal ridge rounded, only moderately distinct for a distance of 
20 millimeters posterior to the beak along which the cardinal surface 
of the shell is more or less flattened horizontally. Posteriorly, the 
umbonal ridge becomes almost obsolete, being indicated by a slight 
flattening of the postumbonal slope. Posterior outline probably as 
in other specimens of Pholadomorpha pholadiformis. 
A part of the original shell substance is preserved. The thick- 
est part of the right valve is found in the area extending from the 
cardinal margin downward for a distance of 10 millimeters from a 
point 10 millimeters anterior to the beak, where the thickness is 
