1910.] The Chalicotheres. 399 



Artioilactyls. The magnum of Chalicotheres, akhoiiojh hij^hly mo(Hfied 

 in form, is fundamentally similar to that of Palcjeosyops and its allies. Every 

 facet in the more i)rimitive type is represented in distorted form in the 

 Chalicotheres, while the posterior hook or toe of the magnum, a frequent 

 Perissodactyl feature, is represented by the whole posterior part of the bone 

 in the Chalicotheres. This comparison of the magnum with that of PalxE- 

 osyops is however not altogether convincing, since the Chalicothere magnum 

 might have been derived independently from that of Euprotogonia. 



(5) As stated above (p. 375) Ameghino associates with the Ancylopoda 

 the genus Homalodotherium of the Santa Cruz beds (Miocene) of Pata- 

 gonia, apparently because the latter has deeply fissured claw-like ungues 

 and the first and second phalanges tend to coalesce, as in Chalicotheres. 

 But this is the kind of adaptive resemblances to other groups which the 

 extinct South American orders so frequently present and it is accompanied 

 by important differences throughout the skeleton. The second metacarpal 

 of Moropus and the corresponding ungual phalanx are greatly hypertrophied, 

 but according to Ameghino's figures, no trace of this peculiar feature is seen 

 in the five-toed Homalodotherium. The carpus of Moropus is high, as 

 in Perissodactyls, that of HomaJodoiheriu.m broad as in Proty pother ium 

 (figured by Sinclair, 1908, p. 71) among the Typotheres. The astragalus of 

 Homalodotherium as figured by Gaudry (1906.1, p. 28, fig. 47) is widely 

 different from that of Moropus and the same is true of the humerus (which 

 retained an entepicondylar foramen. Cf. Gaudry, /. c, p. 9, fig. 8). 



(6) The astragalus of Moropus, while superficially resembling that of 

 Tiianotherium, differs in this important respect, that as noted by Peterson, 

 it has no contact whatever with the cuboid. As the astragalo cuboid con- 

 tact is a progressive feature in the Titanotheres and Rhinoceroses, this 

 joins Avith other evidence to show that the Chalicotheres probably diverged 

 from the other Perissodactyls before the astragalo-cuboid contact became 

 fLxed, i. e., probably much before the Middle Eocene. 



(7) The Chalicotheres resemble the Lower Eocene Condylarth Men- 

 iscotherium in a number of characters enumerated by Osborn (1893, pp. 

 118-133), especially in the form of the top of the skull and the characters 

 of the dentition. In both groups the molars are buno-lopho-selenodont, the 

 metaconule ridge is confluent with the hypocone, both lack the third lobe on 

 nig, both have reduplicate metaconids. However, there are also important 

 differences: e. g., the proto- and metaconules in Meyiiseotherium. show no 

 tendency to join the ectoloph as they do in all the Chalicotheres, the proto- 

 conule in Meniscotherium is V-shaped, not lophoid; the reduplication of the 

 metaconid is equally characteristic of Lambdotherium and Eohippus; in 

 fact, the Chalicothere dentition may be derived as well from the Eower 



