26 Cincinnati Society of Natural History. 



of a fourth plication near the hinge hne. The hinge hne 

 is distinctly shorter than the width of the shell across the 

 middle. The crural plates are strongly developed, and the 

 ridge in the cavity between these plates, representing the car- 

 dinal process, is distinctly indicated by a depression along 

 the middle of the cast of this cavity, as presented by the spec- 

 imen figured, but this depression is not indicated in the accom- 

 panying drawing. 



West Union bed, in the quarry in the southeastern corner 

 of West Union, Ohio. 



Since only a single specimen of PlatystropJiia was found, 

 it is doubtful whether an even number of plications is a con- 

 stant feature of this species. However, the greatly reduced 

 number of lateral plications is probably a feature which may 

 be expected in other specimens from the same locality. 



A single, poorly preserved specimen of PlatystropJiia. 

 from the Osgood bed, south of Nebraska, Indiana, shows 3 

 plications in the sinus and 7 or 8 lateral plications on each 

 side. No other specimens from this horizon are at hand. 



In the Waco limestone member of the Crab Orchard for- 

 mation, at Waco. Irvine, and Panola, in Kentucky, the variety 

 PlatystropJiia reversata, Foerste, is represented by specimicns 

 beginning with two plications in the sinus, increasing to from 

 5 to 8 plications on the larger individuals. 



PlatystropJiia is cited by Orton from the Springfield lime- 

 stone, at Springfield, Ohio. It is not known from the Waldron 

 bed of Indiana, Kentucky, or Tennessee. In the lower part 

 of the Louisville limestone it is represented by a medium- 

 sized species with 5 plications on the fold of mature speci- 

 mens, with 7 lateral plications on each side. PlatystropJiia 

 occurs also in the Louisville limestone at Bledsoe, in Ten- 

 nessee. It has not been found at any horizon in the Browns- 

 port formation. ^ 



PlatystropJiia is fairly common in the Clinton or Brass- 

 field limestone of Ohio, Indiana and Kentucky, and occurs 

 much more sparingly in the overlying Osgood and Crab 



26 



