212 
Aug. F. Foerste 
usually is less strongly geniculate anteriorly^ and the concentric 
wrinkles are less conspicuous, often becoming nearly obsolete 
toward the beak. 
Strophomena maysvillensis, sp. nov. 
{Plate IV, Figs. 13 A, B,) 
The type specimen of Strophomena planoconvex a., preserved in 
the American Museum of Natural History in New York City, is 
labeled as coming from Cincinnati, Ohio. Shells of this type are 
found at Cincinnati at the base of the Fairmount, at the line of 
contact with the Mount Hope bed. They are characterized by 
the moderate convexity of the brachial valve and the slight con- 
vexity of the pedicel valve. The shell is either subquadrate in 
outline, with the hinge line only slightly longer than the width 
across the middle of the shell, or the length of the hinge line is 
distinctly greater and the outline is more nearly semicircular. 
The muscular markings on the interior of the pedicel valve are 
not deep, and the shell is only slightly thickened on the interior 
of this valve. 
In the case of Strophomena maysvillensisy the types of which 
were found in the lowey^ Fairmount at M ays ville,_ Ky., the shell 
usually is larger and rerati\ny fongeF THTTonvexity of the 
brachial valve is greater. The outline frequently is subtriangular, 
the brachial valve being more or less nasute anteriorly. The 
shell is distinctly, though not very strongly thickened along the 
anterior and lateral parts of the interior of the pedicel valve. 
This thickening does not reach the actual margin of the shell and 
is crossed by short though distinct radiating vascular markings. 
Strophomena maysvillensis is very abundant in the lower part of 
the Fairmount in all parts of Kentucky and in Adams county, 
Ohio. In the more western parts of Ohio and in Indiana, Stroph- 
omena planoconvexa is more common at this horizon. At Will- 
iamstown, Paint Lick, and various other localities in western 
Kentucky, Strophomena maysvillensis is common at the base of 
the Fairmount and Strophomena planoconvexa is found in smaller 
numbers at a higher horizon in the same bed. Strophomena 
maysvillensis makes its first appearance in the lower part of the 
Mount Hope in Kentucky, occurring at this horizon in by far the 
greater part of the Ordovician areas, especially east and along 
