272 



January 13, 1853. 

 COLONEL SABINE, Treas., V.P., in the Chair. 



The Earl Granville was elected a Fellow of the Society. 



A pajjer was read, entitled "Description of some species of the 

 extinct genus Nesodon." By Professor Owen, F.R.S. Received 

 Nov. 25, 1852. 



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 Nesodon 

 ovhius. 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 behind 

 this, in both the upper and the lower jaw^s, whence the author con- 

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

 the permanent series was fully developed, viz. i ~|, c J-^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 shovv^ 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 

 American herbivores are shown to agree with each other in characters 

 of greater value, derived from the osseous and dental systems, than 

 any of those by which the Nesodon resembles either the Perissodac- 

 tyle or Artiodactyle divisions of hoofed animals. 



The genus Nesodon is characterized by the following modifications 

 of the teeth, which in number and kind are according to the typical 

 dental formula above given. Incisors trenchant, with long, slightly 

 curved crowns, of limited growth : canines small, not exceeding in 

 length the contiguous premolars. Molars, in the upper jaw, with 

 long, curved, transversely compressed crowns, which contract as they 

 penetrate the bone and ultimately develope fangs ; the outer side of 

 the crown ridged, the inner side penetrated by two more or less 



