1010.] The Homalodotheres; Notostylops. 375 



Amblypods and Proboscideans. The astragalus of Albertogandrija may 

 thus have been derived as above described, from the type retained in the 

 Miocene Homalodotherium, which in turn seems to be derived from the 

 Condylarth, or in respect to its dorsal portion from the Periptychid, type. 



The Homalodotheres probably represent a very old branch of the 

 South American ungulate group, as suggested by the following considerations : 

 (1) The oldest Patagonian formations (?Basal Eocene) yield certain 

 genera, which are in some respects already highly specialized, but which, 

 as argued above, probably belong to this group. (2) The Miocene (?) 

 Homalodotherium' retains the complete Placental formula in the dentition, 

 and five digits in the manus and pes, at a time when most of the allied groups 

 had undergone various reductions in the number of the teeth and feet. 



The ungues of Homalodotherium (cf. Ameghino, 1898, figures on p. 

 175 et seq.) are large, compressed and clawlike, recalling those of the Ancylo- 

 poda, and also tending, as in that group to coalesce with the second row of 

 phalanges. Apparently upon these grounds Ameghino (1898) refers Homa- 

 lodotherium to the Ancylopoda; but evidence is adduced below (p. 399) 

 to show that the resemblances in question probably indicate convergent 

 evolution; and certainly in the palatal aspect the skull of Homalodothe- 

 rium segovice, as figured by Ameghino (1898, p. 173, 1906, p. 317, fig. 134) 

 differs in very important details from the skulls of the Ancylopod genera 

 Chalicotherium and Moropus. 



The Notostylopido'. 



The genus Notosti/lops of Ameghino gives its name to the oldest mammal- 

 bearing horizon of the Patagonian series. Ameghino (1906) places this 

 formation in the Middle Cretaceous but other eminent palaeontologists 

 (e. g., Gaudry, 1908) are inclined to regard it as not older than Basal Eocene. 

 As figured by Ameghino (1906, p. 346) Notosti/lops is seen to be specialized 

 in respect to its enlarged median incisors (i^), reduced i", i^ and canine, and 

 molariform \y^, p^ The upper molars are becoming hypsodont; they have 

 a flat ectoloph, a median valley, a more or less central protocone continuous 

 with the protoconule, and a hypocone continuous with the metaconule; both 

 conules in the slightly worn tooth connect with the ectoloph. These details 

 are more clearly shown in certain less specialized molars of the same general 

 type from the same beds {e. g., Acoclodus Ameghino, 1906, p. 311). They 

 have evidently been derived from a trigonal type possibly resembling in a 

 general way that of the smaller Periptychidse. 



The pterygoid, glenoid and squamosal regions recall those of Hyrax and 

 Protypotherium, the bullae were much inflated. On the ground of very 



