TOAODOUTID^E. 167 



M. 2707. Cast of the right femur. 



Presented by the Royal College of Surgeons. 



43233. The distal half of the left femur ; from the Pleistocene of 

 Buenos Ayres. Presented by Senor L. J. Fontana, 1871. 



40085. The right calcaneum ; from the Pleistocene of Buenos Ayres. 



Purchased, 1860. 



M. 2708. Cast of the right astragalus. 



Presented by the Royal College of Surgeons. 



M. 27Q9. Cast of a middle cervical vertehra. 



Presented by the Royal College of Surgeons. 



The serial position and the right to distinction of the three following 

 Suborders is provisional, and subject to future revision. 



Suborder TOXODONTIA. 



The members of this group, which is provisionally regarded as of 

 subordinal value, present extremely generalized characters. Thus 

 Nesodon shows indications of affinity with the Perissodactyla by its 

 dentition ; Toxodon is related to the Artiodactyla by its cranium, 

 and with the Proboscidea, and perhaps Amblypoda, by its foot- 

 structure ; while Typotherium has considerable resemblance to a 

 rodent. The femur of Toxodon has no third trochanter, and the 

 fibula articulates with the calcaneum. Cope 1 suggests affinity with 

 the Condylarthra and Hyracoidea, the structure of the carpus being 

 apparently similar (vide infra, p. 172). 



Family TOXODONTID^E. 



Genus NESODON, Owen ">. 



Dentition : 1. 1, C. j, Pm. |, M. |. The dentition of this genus 

 connects Toxodon with Homalodontotherium and Macrauchenia. 

 The incisors have short crowns, and the true molars a complex, 

 rhinoceroid structure. The limb-bones are unknown. Four species 

 are recognized by H. Gervais and Ameghino 3 . 



1 Proc. Amer. Phil. Soc. vol. xx. p. 444 (1882). 



2 Eep. Brit. Assoc. for 1846, p. 66 (1847). 



3 Mammiferes Fossiles de I'AmSrique Meridionals, pp. 105-107 (1880). 



