I37 6 CLASS MAMMALIA. 



elongated, with a small brain-cavity, projecting nasals, and a pair of 

 stout transversely placed prominences on the fronto-nasal region. 

 A form to which the name Dceodon has been applied is distinguished 

 by the larger canines. It has been suggested that the American 

 Meniscotherium and the European Hyracodontotherium should be 

 placed in this family. 



Family Macraucheniid^e. — Here may be placed this remark- 

 able family, which presents extremely generalised characters in the 

 vertebrae and limb-bones, such as are unknown in any other mem- 

 bers of the suborder, on which account some writers think it ought 

 not to be included in the Perissodactyla. In the typical Macrau- 

 chenia from the Pleistocene of South America the dentition is 



I. -, C. ~, Pm. -, M. - ; the cheek-teeth are Rhinocerotine in 



3i43 

 structure, the upper molars showing two external V-shaped dentine 

 surfaces and two transverse ridges ; while there is only a very small 

 diastema in the lower jaw. The cervical vertebrae resemble those 

 of the Camelid(z in the position of their arterial canal. The fibula 

 articulates with the calcaneum (as in the Artiodactyla), and there 

 are three digits in each foot, of which the lateral ones are of large 

 size. The incisors have a deep coronal infolding of the enamel, as 

 in the Equidce; and Dr Hermann Burmeister thinks that the muzzle 

 was produced into a short proboscis. The type species is M. pata- 

 chonicha; an allied form from the infra-Pampean beds of Argentina, 

 named by Bravard Palceotherium paranense, is referred by Dr Bur- 

 meister to this genus, but has been made the type of a distinct 

 genus by Dr Ameghino, under the name of Scalibrinitherium Bra- 

 vardi. M. minuta from the same deposits is made by the latter 

 writer the type of Oxydontotherium ; and the name Mesorhinus is 

 applied to yet another form from the same area. Here also may be 

 noticed Theosodon from the above-mentioned deposits, which is 

 placed by Dr Ameghino in this family, although it may be allied to 

 Homalodontotherium, which is also placed here by that writer. 



Suborder 3. Toxodontia. — This group includes a number of 

 very aberrant and generalised Ungulates from the Tertiaries of South 

 America, which present affinities to the Perissodactyla, Proboscidea, 

 and Rodentia, and consequently render it almost impossible to draw 

 up any distinctive diagnosis. 



Family Toxodontid^e. — Nesodon from strata of unknown Ter 



tiary age in Patagonia has its dental formula I. -, C. -, Pm. - M. ~ . 



3i 4 3' 



the incisors having short crowns, and the true molars a complex 

 Rhinoceroid structure, and thus connecting the dentition of Macrau- 

 chenia and Homalodontotherium with that of the next genus. The 

 small N. ovinus was about the size of a Sheep ; but its limb-bones 



