1857.] O^VEN — DICHOBLNE OVINA. 257 



figured in my ' British Fossil Mammals,*' the Dichobune ovina differs 

 in the absence of the basal cusps of the inner cones of the true 

 molars, and by the greater antero-posterior extent of the third molar, 

 due chiefly to the greater proportional size of the hinder supple- 

 mental division of that tooth. The antero-posterior extent of the 

 three true molars is 1 inch 2j lines (0"^'031) in Dich. cervina ; it is 

 1 inch 4^ lines (0™"035) in Bich. ovina. 



The first and second true molars of the lower jaw are so nearly 

 similar in size in the above two species, that the upper molar from 

 the Eocene limestone of Binstead, Isle of Wight, of a true Die hob uney 

 figured and described by me in the ' Proceedings of the Geological 

 Society,' May 20th, 1846 (Quarterly Journal, vol. ii. p. 420), may 

 belong to the present species (Dichobune ovina). And this will be 

 the more probable, should upper molars of the generic type of Di- 

 chodon, answering in size to the lower molars of the Dich. cervina, 

 be hereafter discovered in the freshwater marl at Binstead. 



I proceed next to offer a few remarks on the genera Xiphodo7i and 

 Dichobune, Cuv., and on the first appearance of true Ruminants in 

 the fossil world, which have been suggested in the course of the 

 comparisons instituted for the determination of the above-described 

 lower jaw and teeth of Dichobune ovina. 



Genus Xiphodon. 



The genus Xiphodon was indicated, and its name proposed, by 

 Cuvier, for a small and delicate, long- and slender-limbed Anoplo- 

 therian animal, which, in his first Memoir, ' Annales du Muse'um ' 

 (t. iii. p. bb, 1803), he had called Anoplotherium medium ; but he 

 altered the name, in the second 4to edition of the 'Ossemens Fossiles' 

 (tom.iii. pp. 69 & 251, 1822), to that oi Anoplotherium gracile^-. 



The distinction indicated by Cuvier is now accepted by Palaeonto- 

 logists as a generic one, and a second species {Xiphodon Geylensis) 

 has been added by M. Gervais (Paleontographie Francaise, 4to, 1845, 

 p. 90) to the type-species, Xiphodon gracilis, of which he figures an 

 instructive portion of the dental series of both jaws, obtained from 

 the lignites of Debruge, near Apt. The dental formula o^ Xiphodon 



' i.1,^ -1 • 3-3 1-1 4-4 3-3 .A 



IS the typical one, viz. ^—^, c^— j, p j^^, m ^—^ = 44. 



The teeth are arranged in a continuous series in both jaws. The 

 canines and first three premolars have the crowns more extended 



ciete Geologique de Londres nous a conduit a penser qu'elle appartient au genre 

 Bichodon, que M. R. Owen a etabli pour une autre espece du meme depot, le 

 D. ciispidatus." — Zoologie et Paleontologie Francaise, 4to, pi. 35. Descript. p. 5. 



* Page 440, fig. 181. 



t " Elle differe assez des deux premiers Anoplotheriums par les molaires, les 

 anterieures toutes tranchautes, les posterieures d'en bas a croissans redoubles et 

 paraDeles, pour former un sous-genre dans ce genre; et suivant un usage que j'ai 

 introduit dans raes ecrits zoologiques et dont je reconnais chaque jour davantage 

 I'utilite, j'imposerai a ce sous-genre un nom particulier, Xiphodon, que je tire de 

 la forme tranchante d'une partie de ses dents, de ^ifos et d'ocoys." — Ossemens 

 Fossiles, ed. cit., torn. iii. p. 62. 



