Royal Society, %\\ 



nomenon. Miiller, he believes^ has overlooked the dependence 

 last mentioned. The concluding sentence above cited, " All the 

 circumstances point to the conclusion,^^ &c., is not at all disputed, 

 but is rather a necessary consequence of the more speedy abs- 

 traction of heat by the hydrogen ; for the colder wire presents 

 a less resistance, and hence, as the current is the same in both 

 wires, a less quantity of heat must be developed in the wire, 

 which is preserved cool by its surrounding gas, than in the 

 other. 



XXXV. Proceedings of Learned Societies, 



ROYAL SOCIETY. 

 [Continued from p. 140.] 



Jan. 13, A PAPER was read, entitled "Description of some species 

 1853. -^ of the extinct genus JVesoflfow." By Prof. Owen, F.R.S. 

 The author commences by referring to a genus of extinct herbi- 

 vorous mammals which he had founded in 1836, on certain fossil 

 remains discovered in Patagonia, and which, from the insular dispo- 

 sition of the enamel folds characteristic of the molar teeth, he had 

 called Nesodon. Subsequent transmissions of fossils from the same 

 part of South America, by their discoverer, Capt. Sulivan, R.N., now 

 enabled the author to define four species of the genus. The first 

 which he describes is founded on a considerable portion of the cra- 

 nium and the lower jaw, with the teeth, and is called JNesodon 

 ovinus. After the requisite osteological details and comparisons the 

 author proceeds to describe the three incisOrs, the canine, and five 

 molar teeth, which are present on each side of both upper and lower 

 jaws, and then enters upon an inquiry as to the nature and homo- 

 logies of the grinding teeth. The result is to show that the first 

 four molars belong, with the incisors and canines, to the deciduous 

 series, and that the fifth molar is the first true molar of the perma- 

 nent series ; the germ of a second true molar was discovered biehind 

 this, in both the upper and the lower jaws, whence the author con- 

 cludes that the Nesodon ovimis had the typical number of teeth when 

 the permanent series was fully developed, viz. i ^~, c |^J, p '^~ 



The structure of the grinding teeth proving the extinct animal to 

 have been herbivorous, the number and kinds of teeth in the entire 

 series show that it was ungulate. In this great natural series of mam- 

 malia the author next shows that the Nesodon had the nearest affi- 

 nities to the odd-toed or Perissodactyle order amongst the existing 

 species ; but certain modifications of structure, hitherto peculiar to 

 the even-toed or Artiodactyle Ungulates, are repeated in the cranium 

 of the Nesodon : more important marks of affinity are pointed out in 

 the Nesodon to the Toxodon : and both these extinct forms of South 



