226 
Aug. F, Foreste 
specimen in the Royal Museum at Berlin, in 1838, stated that j 
this specimen had 5 plications in the sinus. Moreover, in our ! 
specimens the sinus and fold appear respectively less deep and ! 
elevated, and the bounding surfaces less vertical than in speci- 
mens referred to Platystrophia hiforata by Curt Gagel. Unfor- 
tunately very different forms have been referred to Platystrophia 
hiforata at various times. The type of that species appears never 
to have been figured, and it seems to have been lost. 
Platystrophia ponderosa — auburnensis^ nom, nov. j 
. {Plate IF, Fig. 15.) 
The type of this variety was found in the Mount Auburn bed j 
at Lebanon, Ohio. The variety is fairly common at the Mount 
Auburn horizon at Cincinnati, and at other localities in Ohio, j 
It may be regarded as characteristic of that horizon, but does not | 
exist there to the exclusion of Platystrophia ponderosa^ of which 
it may be regarded as a more gerontic form. It is more globose, j 
and has a distinctly shorter hinge line. As a rule the shell is 
narrower and the number of lateral plications is less, sometimes [I 
not exceeding 5 or 6, becoming obsolete toward the posterodaterai j 
angles. | 
This variety appears to be closely related to Platystrophia lynx^ \ 
Eichwald, as identified and figured by Curt Gagel. Eichwald 
describes the median fold of Platystrophia lynx as having 4 grooves j 
so that there should be 5 plications. Von Buch states regarding i 
the same species that it had 4 plications in the sinus and on the j 
fold, and 9 plications on each side. The specimens figured by ] 
Curt Gagel as Platystrophia lynx are relatively longer, the fold ji 
and sinus are more abrupt, and the lateral plications are more | 
numerous, and more distinct toward the postero-lateral angles j 
than in the forms selected as types of Platystrophia ponderosa- j 
auhurnensis. j 
It is possible that the specimens figured by Platystrophia || 
lynx, in volume i of the Ohio Paleontology, were obtained from | 
the Mount Auburn horizon, but they do not have as short a hinge 
line as the variety here illustrated, they are less globose, and the 
lateral plications are more numerous and more distinct postero- 
laterally. 
The type of Platystrophia lynx as described by Eichwald ap~ j 
