260 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 11, 



clearly show that the hinder division of the upper true molars was 

 complicated by the additional (third) cusp. So far as I have any 

 knowledge of the specimens, or recorded specimens, of Bichobuney 

 there are no better grounds than analogy for determining which is 

 the fore and which the back part of the detached upper molar teeth. 

 According to the Anoplotherium and Xiphodon, the three-cusped 

 division would be the front one ; according to the Microtherium, it 

 would be the hind one. The modification of the molar described 

 and figured in the ' Quarterly Geological Journal,' vol. ii. p. 420, is 

 such, as, from subsequent knowledge of the teeth of extinct Artio- 

 dactyles, to confirm me in the choice of the analogy of the Anoplo- 

 therium, in determining the fore and back parts of the crown of that 

 upper molar. 



With regard to Microtherium, the unusually perfect fossil skulls 

 of that small Herbivore, which did not exceed in size the delicate 

 Chevrotains of Java and other Indo-Archipelagic Islands, e. g. Tra- 

 galus Kanchil, are of importance in regard to the question of the first 

 appearance of the Ruminantia, on account of the demonstration they 

 give of the persistent and functional upper incisor teeth. The little 

 Eocene even-toed Herbivores, like the larger Anoplotherioids, thus 

 departed from the characters of the true Ruminants of the present 

 day, in the same degree in which they adhered to the more general 

 type of the Artiodactyles. Had M. de Blainville possessed no other 

 evidence of the Microtherium than of the Dichobune murina and 

 Dichobune obliqua, Cuv., he would have had the same grounds for 

 referring the Microtheria, as the Dichobunes, to the genus Tragulus or 

 Moschus (les Chevrotains) : but the entire dentition of the upper jaw 

 of the species Anoplotherium murinum and A. obliquum, referred by 

 Cuvier to his genus Dichobune, must be known, before the existence of 

 Ruminants in the Upper Eocene gypsum of Paris can be inferred. 



No doubt the affinity of these small Anoplotherioids to the Chevro- 

 tains was very close. Let the formative force be transferred from 

 the small upper incisors to the contiguous canines, and the transition 

 would be effected. We know that the Ruminant stomach of the 

 species of Tragulus is simplified by the suppression of the psalterium 

 or third bag : the stomach of the small Anoplotherioids, whilst pre- 

 serving a certain degree of complexity, might have been somewhat 

 more simplified. The certain information which the gradations of 

 dentition displayed by the above-cited extinct species impart testifies 

 to the artificial character of the Order Ruminantia of the modern 

 systems, and to the natural character of that wider group of even- 

 toed hoofed animals for which 1 have proposed the term Artio- 



DACTYLA. 



DESCRIPTION OF PLATE VIII. 

 Lower jaw and teeth of Dichobune ovina, nat. size. 



Fig. 1. Upper view, showing the grinding and cutting surfaces of the teeth j 



ideal outlines of the four anterior incisors are added. 

 Fig. 2. Outside view of the lower jaw and teeth. 

 Fig. 3. Inside view of the teeth. 



