HISTORY OF THE t^STRAPOTHERIA 509 



it had a very long history. It has not been found in any for- 

 mation later than the Santa Cruz, unless the Friasian fauna, 

 which contains it, should be removed from that stage, of which 

 it apparently forms the latest division. 



I. fASTRAPOTHERIID^. 



^Astrapotheriimi, Santa Cruz and Patagonian. ^ Astrapothericulus, 

 Patagonian. '\ Parastrapotheriiwi, Deseado. \Astraponotus, Astra- 

 ponotus Beds. \ Alhertogaudrya, Casa Mayor. 



II. fTRIGONOSTYLOPID^. 



t Trigonostylops, Casa Mayor, f Edvardocopeia. Astraponotus Beds. 



The genus ^Astrapotherium, which was the only well-de- 

 fined representative of its family and order in the Santa Cruz 

 stage, contained several species, some of them the largest 

 animals of their time, as well as the most grotesque in appear- 

 ance. The dentition differed in some important respects from 

 that of all the other South American ungulates, the formula 

 being : z f , c ^, p f , m |, X 2 = 28. The upper incisors had com- 

 pletely disappeared, but the lower ones were large and, what 

 was an exceptional character, they were partially divided into 

 two lobes, somewhat as in the Eocene fuintatheres of North 

 America (p. 446). The canines were very large and formi- 

 dable tusks, which grew throughout life and apparently formed 

 no root ; the upper tusk was nearly straight and was obliquely 

 truncated by the strongly curved and sharp-pointed lower 

 tusk. This arrangement was very unusual among South 

 American hoofed mammals, many of which had no tusks at all ; 

 and in those which possessed them, such as the ftoxodonts 

 (p. 468), they were mostly incisors. Only in the fastrapotheres 

 and fhomalodotheres were there canine tusks, and in the latter 

 group they were small and of limited growth. All the teeth, 

 except the canines, were brachyodont and, though rather high- 

 crowned, formed roots before coming into use. The pre- 

 molars were small and greatly reduced in number (|), and in 

 pattern were simpler than the molars. The upper molars were 

 constructed on essentially the same plan as in the fToxodonta ; 



