III.] MARSUPIALS. 1 1 1 



confined to the Santa Crucian horizon, where it is represented by 

 the family Abderitidce, the last premolar in each jaw is much 

 larger and taller than the other teeth, and has its crown in the 

 form of a compressed cone, marked on the sides with vertical 

 grooves, as exhibited in the figure of Abderites. A third family is 



FlG. 27. RIGHT HALF OF LOWER JAW OF Abderites, MUCH ENLARGED. 



known as the Garzoniidce. In all the skull is of an elongated 

 form, with large vacuities both in the front and hinder part of the 

 palate, and presents a considerable general resemblance to those 

 of the Australian genera Peragale and Perameles. With the ex- 

 ception of the retention of four pairs of upper incisors and the small 

 size of all these teeth, the dentition exhibits, however, a remark- 

 able approximation to that of the Australian diprotodont genus 

 Dromicia. On the other hand, the feet are of normal structure, 

 with five complete toes, none of which are united by integuments; 

 the thumb and great toe being apparently slightly opposable to 

 the other digits. Probably the rat-like tail is slightly prehensile 

 at the extremity ; and a small pouch is present in the female. In 

 the skeleton the lower jaw exhibits the usual inflection of the 

 angle ; and the pelvis carries marsupial bones. 



Probably these Patagonian marsupials, which may be known 

 as selvas, must be included in the diprotodont sub-order ; from 

 the Australian representatives of which they differ by the small 

 and numerous upper incisors and the non-syndactylous hind feet. 

 Both these being generalised features, it is evident that if the 

 selvas are true diprotodonts their ancestors must have originated 

 from the polyprotodonts in Notogaea, for if they are of exclusively 

 South American origin they must form a subordinal group by 



