LOPHIODONTID2E. 13 



Big-Horn River, Wyoming, U.S.A. This and the next 

 specimens agree with those figured by Cope in the Rep. 

 U.S. Geogr. Surv. W. of 100th Meridian, vol. iv. pt. ii., 

 Palaeontology, pi. Ixvi. figs. 1-6 (1877). 



Presented by R. Lydekker, Esq., 1885. 



Jffi, 2561 a. Three fragments of the mandible, associated with the 

 preceding. Presented by R. Lydekker, Esq., 1885. 



Genus PACHYNOLOPHUS, Pomel l . 

 Syn. Lophiotherium, P. Gervais 2 . 



Propalceotherium, P. Gervais 3 . 



Dentition : I. |, C. \, Pm. |, M. ^. The upper true molars have 

 higher ridges than in Hyracotherium, and are intermediate in 

 structure between those of the latter and those of Anchilophus ; the 

 lower true molars are subcrescentoid. The genus occurs both in 

 Europe and North America. 



Pachynolophus isselanus (Blainville) 4 . 

 Syn. Palfsotherium isselamim, Blainville 5 . 



Propalceotherium isselanum, P. Gervais 6 . 



This species is of comparatively large size. 

 Hob. Europe. 



tfig. 4. 



Pachynolophus isselanus. The third left upper true molar ; from the Middle 

 Eocene of Issel. \. Letters as in fig. 1. (From Gaudry's ' Enchaine- 

 ments '). 



1 Arch. Sci. Phys. Nat. vol. iv. p. 327 (1847). 



2 Zool. et Pal. Francises, 1st ed. vol. i. p. 56 (1848-52). The writer follows 

 Gaudry (' Les Enchainements &c. Mammiferes Tertiaires,' p. 68) in uniting 

 Lophiotherium and Propalceotherium with Pachynolophus. 



3 Comptes Rendus, vol. xxix. p. 383 (1849). 



* Osteographie, Genus Pal<eotherium, pi. viii. (1846) ; Palaotherium. 



5 Loc. cit. 



6 Zool. et Pal. Frances, 2nd ed. p. 115 (1859). 



