74 



SINCLAIR— THE SANTA CRUZ TYPOTHERIA. 



[April 24, 



it is even more so to determine their degree of kinship with Typo- 

 therium. From their small size it seems quite probable that none of 

 the Santa Cruz Typotheria are in the direct line of descent culmi- 

 nating in this genus. This is confirmed by the degree of specializa- 

 tion in dentition and foot structure which Typotherinm displays. 

 The teeth of the latter show a greater complexity of folding than is 

 attained by any of the Santa Cruz typotheres, while the feet are less 

 specialized with a pollex in the manus which has been lost in Pro- 

 typotherium, the most generalized of the Santa Cruz typotheres 



ac...} 



B 



ac. 



Fig. 9. A. Unworn third lower molar of a young Protypothcrium, four 

 and one half times the natural size. (No. 9482 American Museum of Natural 

 History collection.) B. Nesodon hnhricatiis Owen, two lower molars, three 

 fourths the natural size. (No. 15135 Princeton University collection.) ac, 

 anterior crescent; pc, posterior crescent; pp, posterior pillar. 



(Fig. 6, A), and with digit V. of the pes less reduced than in the 

 most specialized of the latter (Pachyrukhos) . A pollex has been 

 figured by Ameghino^ in the manus of Pachyrukhos typicus, but 

 none has been fottnd in any Santa Cruz specimen. The manus in 

 Hegetothcrinrn is unknown, so the above statement regarding the 



"^ Ameghino, Florcntino, " Contrib. al conoc, etc.," PI. 13, fig. 14. 



