a O/4 [March 7, 
Cope. | 
Agriochcrus guyotianus; A. trifrons, sp. nov. ; A. ryderanus. Coloreodon 
macrocephalus. 
North Fork of John Day River Epoch. ucrotaphus trigonocephalus, 
sp. nov. ; H major, Coloreodon ferox ; C. macrocephalus. 
Ticholeptus Beds. Merycocherus montanus, sp. nov.; M. rusticus; M, 
proprius. Merychyus arenarum, sp. nov. ; M. pariogonus, sp. nov. ; M. 
zygomaticus. Oyclopidius simus; C.emydinus, sp. nov. Leptauchenia 
major; L. decora; L. nitida. Pithecistes brevifacies; P. heterodon; P. 
decedens, sp. nov. 4 
Loup Hork Beds. % Merychyus elegans ; M. medius; ? M, major.* 
The stratigraphic relations of these species may be represented under 
their generic heads in the following table : 
Ades al sea z 
Poe aoe ieee 2 Bact 2 a 
|e | Ae A'S onl oS "9 
[ae a a a ee Se ee 
| 6 bal | acs] | im} a} 
[ees i A eC be KS "oO fx & 
ie| ee . 
Oreodontina. | 
Oreodon Leidy........, 3 |———| 
Eucrotaphus Leidy....| § 
Merycocheerus Leidy..| 7 | 
Merychyus Leidy...... Beals, eee mnt 
Leptauchenia Leidy ...| Pe eyerged 
Jyclopidius Cope......| 2 beget sopemnarie 
Pithecistes Cope..... Figs aa hseugemecomenn 
Agriochwrine. | 
Agriocherus Leidy. 
Coloreodon Cope 
On the Structure of the Skull in the Elasmobranch genus Didymodus. 
By H. D. Cope. 
(Read before the American Philosophical Society, March %, 1884.) 
The genus Diplodus was described by Agassiz from specimens of teeth 
from the European Coal Measures. In America, Newberry and Worthen 
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 Chlamydoselachus 
* The questions refer to the geological age. 
t Geology of Illinois, vol. il. 
ae 
