72 



SINCLAIR— THE SANTA CRUZ TYPOTHERIA. 



[April 24, 



of Nesodon (Fig. 7, B) is the realization of a structure already fore- 

 shadowed in the pes of Hegetotherium (Fig. y, A). The fifth digit, 

 which is greatly reduced in Hegetotherium; has here disappeared 

 and the ento- and meso-cunei forms have united to a single bone. 

 The shortening of the neck of the astragalus and the increase in 

 size of the fibular facet on the calcaneum are, perhaps, adaptations 

 to the support of weight. Although the molars of Nesodon appear 



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Fig. 7. A. Hegetotherium mirabile Ameghino, right hind foot, three 

 fourths the natural size. (No. 15542 Princeton University collection.) B. 

 Nesodon imbricatus Owen, right hind foot, about one third the natural size. 

 (No. 15460 Princeton University collection.) 



exceedingly complex, owing to the development of secondary enamel 

 folds, the primary elements can be homologised with those displayed 

 in the simpler crown pattern of Protypotherium., as indicated by the 

 similar lettering in Figs. 8 and 9. This comparison can not yet be 



