Cope. 



572 



[March 7, 



Agriochcerus guyotianus ; A. trifrons, sp. nov. ; A. ryderanus. Coloreodon 

 macrocephalus. 



North Fork of John Day River Epoch. Eucrotaplius trigonocephaly, 

 sp. nov. ; E major. Coloreodon ferox ; C. macrocephalus. 



Ticholeptus Beds. Merycochcerus montanus, sp. nov. ; M. rusticus ; M> 

 proprius. Merychyus arenarum, sp. nov. ; M. pariogonus, sp. nov. ; M. 

 zygomaticus. Cyclopidius simus ; C. emydinus, sp. nov. Leptauchenia 

 major ; L. decora ; L. nitida. Pithecistes brevifacies ; P. heterodon ; P. 

 decedens, sp. nov. 



Loup Fork Beds. 1 Merychyus elegans ; M. medius ; ? M. major.* 



The stratigraphic relations of these species may be represented under 

 their generic heads in the following table : 



Oreodontince. 



Oreodon Leidy 



Eucrotaphus Leidy. 

 Merycochoerus Leidy 

 Merychyus Leidy. . . 

 Leptauchenia Leidy 

 Cyclopidius Cope. . . 

 Pithecistes Cope. . . . 



Agriochozrince. 

 Agriochcerus Leidy. 

 Coloreodon Cope . . . 



3 

 3 

 7 

 6 

 3 



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Ow £Ae Structure of the Skull in the Elasmobranch genus Didymodus. 

 By E. D. Cope. 



{Read before the American Philosophical Society, March 7, I884.) 



The genus Diplodus was described by Agassiz from specimens of teeth 

 from the European Coal Measures. In America, Newberry and Worth enf 

 have described four species from the Carboniferous of Illinois and Ohio ; 

 and I have reported two species from the Permian beds of Illinois and 

 Texas. Recently Mr. Samuel Garman has described a shark, said to have 

 been taken in the Japanese seas, under the name of ClilamydoselacJius 



* The questions refer to the geological age. 

 t Geology of Illinois, vol. ii. 



