1910.] Patagoniaii Condylarths (?) and Pcriptychids (?). 373 



of the present work, it seems advisable to attempt a preliminary brief review 

 of the available evidence of their relationships with each other and with 

 other orders. Among the sources of evidence on this subject examined by 

 the writer may be mentioned: first a series of excellent casts representing 

 many Santa Cruz and pre-Santa Cruz ungulates, which has been presented 

 to the American INIuseum bv the Museo Nacional de Buenos Aires through 

 the courtesy of Dr. Fl. Ameghino; secondly the figures given especially by 

 Ameghino, Lydekker, Roth, Scott and Sinclair; thirdly the observations 

 and conclusions of these authors. 



South American Condylarths {'t) and Taligrada^'l). 



Resemblances between the dentition of different forms of unknown 

 ordinal affinities are frecjuently apt to be misleading, as elsewhere noted 

 (p. lOS); but they are not always misleading and in the case of Didolodus 

 and certain other genera {e. (j., Giulielmo flower ia, Ricardolydekkeria) from 

 the Notostylops Beds, described by Ameghino (1904), the resemblances to 

 the Condylarths and Taligrada of the northern hemisphere extend to certain 

 details which seem to indicate affinity; and this indication is strengthened 

 by considerable indirect evidence: e. g., (1) the several plans of limb struc- 

 ture in the Toxodonts, Typotheres and Litopterns seem derivable (pp. 377, 

 379) from the conditions seen in the Condylarthra; (2) the skull of the 

 primitive Litopterns suggests that of Meniscotherium; (3) the astragalus 

 and calcaneum of Trigonostylops (Gaudry, 190G.1, fig. 48, p. 28) is of the 

 IMeniscothere type; (4) the astragalus and calcaneum of all the extinct 

 South American ungulates seem to be modifications either of the tyjiical 

 Condylarth or of the Taligrade types. 



The simple, sexitubercular bunodont upper molars of the ?Basal Eocene 

 Didolodus and its allies may at first appear to bear little relation to the 

 complex hypsodont molar patterns of the Santa Cruz ungulates, etc.; but 

 an examination of the casts and figures already referred to shows that there 

 are several morphological if not genetic intermediates between the two 

 extremes, and that, as noted in detail below (pp. 376, 379), the molar patterns 

 of lyitopterns, Homalodotheres, Astrapotheres, Toxodonts and Typotheres 

 may be analysed with some degree of confidence in accordance with the 

 nomenclature of trituberculy (cf. Osborn, 1907, pp. 189-190). And it may 

 be well to state in this comiection that the writer does not give assent to the 

 theory of trituberculy in certain of its implications; but nevertheless, after 

 returning to test certain basal assvmiptions he feels convinced that all the 

 extinct South American ungulate groups have been derived from forms in 



