426 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 56. 



correspondingly greater number of plications on the lateral slopes, 

 there being from 18 to 30 or more. The acuminate cardinal extremes 

 are so thickened as to be enth-elv filled with shelly deposit. 



Measurements. -43 mm. along the hinge line, 25. (i mm. wide across 

 the middle, 17 mm. high, 15.7 mm. thick, 12 mm. sinal width, 8 mm. 

 sinal depth, 2.8 mm. fold height. 



Occurrence. -R\Q\\vcio\\({ grou]): Whitewater: l^^sually found asso- 

 ciated with typical PlatystropJda acutilirata. 



Plesioty pes. —Cut. No. 65688, U.S.N.M. 



PLATYSTROPHIA ACIITILIR.\TA SENEX Cumings. 



Plate 45, fig. 23. 



Orthisinflata? .]amks, Gut. Lower Sil. Fos. of the Cincinnati Group, 3871, p. 10 



{nomen midem). 

 Orthis hiforata var. acuHlirata Lesley (part) GeoL Surv. Pennsylvania, Kept. 



P. A, 1889, p. 508, figs. 5c, 5/ 

 Platystrophia acutilirata Grabau and Shimer, North American Index Fossila, 



vol. 1, 1907, p. 257, figs, e, g, h, L 

 Platystrophia accvtilirata Cl'mings, Amer. Joiirii. Sci., ser. 4, vol. 15, 1903, p. 35, 



fig. 18 (part). 

 Platystrophia acutilirata var. senex (part) Oumings, 32nd Ann. Kept. Dept. Geol. 



Nat. Res. Indiana, 1908, p. 913, pi. 35, figs. 4a-c. 

 Platystrophia acutilirata inflala Foerste, Bull. Sci. Lab. Denison Univ., vol. 16, 



1910, pi. 4, fig. 8. 



This variety is represented by specimens which possess retrogres- 

 sive characters. It passes through an acuminate development in 

 late neanic and early ephebic stages, and then becomes very convex, 

 the depth often exceeding the height. The thickening of the shell 

 and growth varices are more pronounced than in typical specimens. 

 The change in contour is decidedly marked. 



Measurements. — -35.5 mm. along the hinge line, 38 mm. across the 

 middle, 25 mm. thick, 25.5 mm. high, 14 mm. sinal width, 14.5 mm. 

 sinal depth, 3 mm. fold height. 



Occurrence. — -Richmond group: Upper part of the Whitewater 

 formation : Found associated with PJatystropliia acutilirata. 



Plesiotype. -Qu. No. 65691, U.S.N.M. 



PLATYSTROPHIA ELKHORNENSIS, new species. 



Plate 46, figs. 17-10. 



From the Elkhorn member of the liichmond along Elkhorn Creek, 

 Wayne County, Indiana, were collected two specimens of a short- 

 hinged globose form with a deep sinus and moderately elevated fold. 

 The slopes are abrupt. Those of the brachial valve are regularly 

 convex; those of the pedicle valve are slightly flattened toward the 

 cardinal angles. There are three plications in the smus and four on 

 the fold, the two outer ones in each case being the weakest. There 



