2l6 Bulletin A^nerican Aluseum of Natural History. [Vol. X, 



Prophetic of this type, perhaps, is the pes of Pantolambda 

 cavirictiis (Fig. 12), in which the navicular is reduced upon the 

 outer side and the ectocuneiform is elongated so as to nearly 

 come in contact with the astragalus. 



Foot Structure. 



Cope (i!:^84, I, p. 1 1 20) proposed the theoretical groups, Platy- 

 arthra (with flat astragalus) and Amblypoda Jiyodonia (astragalus 

 without a neck) from which to derive the Amblypoda. Both groups 

 are superfluous now that it is clear that the ancestral Amblypoda 

 can be derived directly from the Creodonta, all of which possess 

 an astragalar neck. 



Pfanes of AstragaJo-tjiual facets 



Fig. 2g. Angles formed by tibio-astragalar astragalo-navicular facets, to exhibit widening 

 of front face of astragalus, l/r, Ursus ; P. Pantolambda ; C, Coryphodon testis : Ui., Uinta- 

 therucm ; E, Elephas. 



The transition is simple. By shortening of the neck of the astra- 

 galus (Fig. 29 P. and C. and Ui) the tibio-astragalar facet is 

 gradually brought almost into confluence anteriorly with the astra- 

 galo-navicular facet, as in C. radians. In C. lobatus and C. sin- 

 gularis this space widens as in Uintatherium. 



I. The variables in these feet are the astragalar foramen and 

 the tibiale facet. From our present knowledge both these struc- 

 tures (inherited in Coryphodon from Pantolambda) are useless or 

 vestigial, inconstantly developed and therefore not constant specific 

 characters. 



In Fig. 26 (identical with Coryphodon III, Cope, 1877, PI. 60), 

 a small astragalus and calcaneum is shown which lacks both astra- 

 galar foramen and tibiale facet. In C lobatus (No. 4335, type of 

 C. pachypus) there is a large tibiale facet, while the astragalar 



