285 



PLATE X Continued. 



Page 



Figs. 22 to 24. Leda inflate Girty mss 205 



After Girty. Morrow formation: Oklahoma. 



Fig. 22. Right valve of a cotype. x2 



Fig. 23. Left valve of same cotype. x2 



Fig. 24. Dorsal view of same cotype. x2 

 Figs. 25, 26. Leda meekana Mark '_ 206 



After Mark. Conemaugh formation: Portersville lime- 

 stone, Portersville, Ohio. 



Fig. 25. Right valve. x4 



Fig. 26. Same, natural size. 

 Fig. 27. Leda bellistriata Stevens 204 



Lower Mercer member: Perry County, Somerset, Lo- * 

 cality 35. 



Left valve. Hyde collection 819. 

 Figs. 28, 29. Leda prolongata n. sp 206 



Fig. 28. Right valve of holotype, not entirely uncovered, 

 slightly enlarged. Lower Mercer member: Muskingum 

 County, Fairview Schoo 1 , Locality 45. 



Fig. 29. Right valve of another more perfect specimen, 

 showing more closely the real outline and convexity of 

 the species, slightly enlarged. Lower Mercer member: 

 Perry County, Somerset, Locality 35. Hyde collection 

 818. 

 Figs. 30, 31. Parallelodon tenuistriatus (Meek and Worthen) 210 



After Mark. Conemaugh formation: Portersville lime- 

 stone, Portersville, Ohio. 



Fig. 30. Left valve showing the average size of specimens 

 from the Lower and Upper Mercer members. 



Fig. 31. Same showing average size of specimens from 

 the Harrison and McArthur members. 



