374 Bulletin American Museum of Natural History. [\o\. XXVII, 



which the upper molars still retained clear traces of the trigonal pattern, 

 while the lower molars retained eciually clear traces of the tuberculo-sectorial 

 |)attern. 



Relations of the Homalodotheres and Astrapothercs. 



As shown above Lydekker grouped "Ho7naIodontotherium" and Astra- 

 potherinm. in a single suborder and in support of this procedure there seems 

 to be considerable evidence: e. g., (1) Ameghino has figured a number of 

 genera (e. g., Albertogaudrga, Astraponotus, Astra pother irulus) in which 

 the upper molar pattern appears to connect the Homalodotheres with the 

 Astrajiotheres. (2) The hyi)sodont lower molars of Albertogaudrya have 

 the trigonid short and the talonid long anteroposteriorly, and they suggest a 

 common origin of the Homalodo there and Astrapothere types. (3) The 

 upper molars of the Homalodotheres, Astrapotheres, Toxodonts and Typo- 

 theres are all broadly of the Rhinocerotic type, /. e., with flattened ectoloph 

 and large protoloph, no mesostyle, a crista. They also have a strongly de- 

 veloped protostyle and hypostyle. (4) The astragalus referred by Ame- 

 ghino to Albertogaiidrija is of the flattened type, which Gaudry (1906.1, p. 

 19) assigns also, on other grounds to Astra potherium. 



Against the association of Astrapotheres and Homalodotheres in a 

 single suborder the following objections might be raised: (1) Astrapotherium 

 is said to lack the dilated condition of the scpiamoso-periotic region; but even 

 if it be shown that in Ilomalodotherium this region is slightly dilated, this 

 will not prove that the two groups are very widely separated; and, partly 

 on account of the variability of such inflation between different families in 

 Marsupials and Rodents, the writer suspects that Dr. Roth has overesti- 

 mated its significance in the South American imgulates. (2) In Astra- 

 potherium the limbs are thought by Gaudry (1900. 1, p. 19) to have been 

 rectigrade, whereas in Homalotherium., as figured by Ameghino (1898, p. 

 175), the feet end in large fissured ungues and were probably semi-planti- 

 grade. But such dift'erences, in the case of the Marsupials (compare 

 Diprotodon and Phalangista) and of the Perissodactyls and Ancylopoda, 

 are not inconsistent with ordinal relationships. 



The astragalus of Albertogaudri/a resembles the Amblypod type in so far 

 as it has suffered a shortening of the neck, which has ended in the virtual 

 disappearance of the latter and the bringing of the navicular facet below the 

 tibial facet or trochlea; but this is probably an indication, not of ordinal 

 affinity with the x\mblypoda, but simply of the assumption of the rectigrade 

 pose of the limbs, which in Pyrotherium, according to Gaudry (1909) like- 

 wise has resulted in the astragalus assuming the general type seen in the 



