310 MAMMALIA. 



Siwalik Formation of India, have also been referred to the 

 same genus. Various limb-bones sufficiently resembling those 

 of Macrotherium have likewise been described from Pikermi 

 and the Island of Samos, under the generic name of Ancylo- 

 therium. These indicate somewhat more robust limbs, of more 

 nearly equal size than those of the Sansan fossil. There are, 

 however, only three digits in each foot. 



Sub-Order 6. Typotheria. 



The Tertiary Formations of South America, especially those 

 of the Argentine Republic, yield skeletons of many strange 

 extinct ungulates which are quite unlike those hitherto found 

 in any other country. These seem to represent at least three 

 distinct sub-orders of which the true relationships are still 

 entirely obscure, but which must be little-modified descendants 

 of very primitive eutherian mammals. 



The members of the first of these South American groups 

 differ from all other known ungulates in the possession of well- 

 developed clavicles. The teeth are deepened and more or less 

 rodent-like ; but the dental series is nearly complete as a rule, 

 only the canines being constantly reduced or absent. The 

 humerus is pierced by an entepicondylar foramen (as in Condyl- 

 arthra and some Rodentia), and the femur has a third 

 trochanter. The radius and ulna (tibia and fibula) are 

 complete and usually separate, and the digits are four or five 

 in number. The sub-order thus briefly characterized is named 

 TYPOTHERIA from Typotherium, the genus first described. Its 

 earliest representatives occur in the Pyrotherium and Santa 

 Cruz Formations of Patagonia, while the latest and largest 

 forms are met with in the Pampa Formation (probably 

 Pleistocene) of Buenos Aires. Most of the earlier genera 

 (e.g., Protypotherium, Icochilus) possess a complete dentition, 

 with the teeth in a regular and nearly continuous series, 

 and the incisors, both above and below, are rooted ; the latest 

 genus from the pampas (Typotherium) has completely lost the 

 canines, while there is a considerable diastema, with only one 

 pair of persistently-growing incisors in the upper jaw, two pairs 

 in the mandible. In the course of evolution it may also be 



