1857.] OWEN PLIOLOPHUS VULPICEPS. 63 



bones ; but in this character, and in the important one of the more 

 simple formation of the nostril, Anoplotherium offers a closer re- 

 semblance to Pliolophus. In the almost straight upper contour of 

 the skull, the Horse and the Hyrax, amongst existing Ungulates, 

 resemble Pliolophus, and both these Perissodactyles add the corre- 

 sponding character of the juncture of the premaxillaries with the 

 nasals, which Pliolophus presents in common with the Anoplothe- 

 rioids. But the orbit is circumscribed by bone in the above-cited 

 existing Perissodactyles, whilst it opens behind into the temporal 

 fossa in both Anoplotherium and P alceotherium, as in Pliolophus. 

 Microtherium resembles the small Musk-deer in the entire bony 

 frame of the orbit. 



The form of the skull in Lophiodon proper has not yet been ascer- 

 tained ; but the comparative simplicity of the premolars in Pliolo- 

 phus, and the configuration of the surface of the upper true molars, 

 especially the last, PL III. fig. 2, m 3, demonstrate that the present 

 small Eocene quadruped has the nearest affinity to the Lophiodont 

 family, amongst the known extinct and recent members of the class. 

 To a Lophiodont mammal, indeed, of the same size from the marls 

 of the ' Calcaire grossier ' in the vicinity of Paris (Lophiodon lepto- 

 gnathum, Gervais *, Hyracotherium de Passy, De Blainville t)> on 

 which M. Pomel subsequently founded his subgenus Pachynolophus, 

 I felt most inclined, at first, to refer the Pliolophus ; and it was in 

 the prosecution of this comparison that I determined to sacrifice the 

 entireness of one side of the fossil skull, in order to obtain a more 

 complete and satisfactory view of the grinding surface of both upper 

 and lower molars than could otherwise be got. 



For the comprehension of the following comparison, PI. II. figs. 3 

 & 4, and PI. III. fig. 2, of the present memoir should be examined 

 by the side of the views of the upper molar teeth and of the right 

 mandible and teeth of the Pachynolophus (Lophiodon) Buvalii,Vomel, 

 which M. Gervais has given in his excellent ' Zoologie et Paleontologie 

 Francaise, 5 4to, pi. 17. f. 1, 1 a & 2. Unfortunately the grinding 

 surface of the upper molars only of Pachynolophus has been figured, 

 and with these I proceed to compare the same teeth of Pliolophus 

 vulpiceps. 



I may premise that the generic or family character of the upper 

 molars in Lophiodon is the development of the outer wall of the true 

 molars and last premolar into two cones, and by the continuation, 

 therefrom, in the true molars, of two oblique ridges which thicken 

 and rise into rather smaller and lower cones on the inner side of the 

 crown. In the last premolar the oblique ridge is continued only 

 from the anterior of the two outer cones, and expands into a single 

 large cone forming the inner half of the crown. 



In Pachynolophus as in Pliolophus the oblique ridges are lower 

 at their commencement, in comparison with their inner terminal 

 cones, than in Lophiodon, and accordingly a degree of attrition 



* Comptes Rendus de l'Acad. des Sciences, Paris, vol. xxviii. p. 547. 

 f Osteographie, Lophiodonts, p. 190. pi. 2. 



