624 LAND MAMMALS IN THE WESTERN HEMISPHERE 



level of the teeth ; the orbit was widely open behind and the 

 descending process given off from the zygomatic arch beneath 

 the eye had no such exaggerated length; the bones were not 

 conspicuously inflated by sinuses. The lower jaw was shal- 

 lower, the symphysis and anterior spout shorter and the as- 

 cending portion far lower. 



(7) The backbone had a greater number of separate parts ; 

 the atlas, as always, was free, the axis was fused with two or 

 three of the following vertebrae; the sixth was free and the 

 seventh fused with the first and second dorsals to form one 

 piece, which was succeeded by two or three separate vertebrae : 

 the other dorsals, except the last one, were united in the dorsal 

 tube, and the lumbo-sacral tube was already complete. Thus, 

 instead of four or five, there were eight or nine distinct parts. 

 None of the tail- vertebrae were fused together. 



(8) There was the same disparity in the length of the fore 

 and hind limbs, but the bones were far more slender and ar- 

 madillo-like ; this was especially true of the radius and hu- 

 merus, the latter having well-developed deltoid and supinator 

 ridges and epicondylar foramen; the ulna was more massive 

 and glyptodont-like. The femur was very much more slender 

 and rounded and the third trochanter was placed higher up 

 the shaft ; tibia and fibula were coossified at both ends and 

 resembled those of the Pampean genera, except for their much 

 greater slenderness. 



(9) The feet were much as in the latter, but relatively nar- 

 rower, and the manus had longer claws. 



In short, the Santa Cruz fglyptodonts departed much less 

 widely from the armadillos than did the Pliocene and Pleisto- 

 cene genera, and, to a certain extent, bridged over the gap 

 between the two suborders. Such backward convergence in 

 time is very strong evidence for the community of origin of 

 the two groups. 



The fglyptodonts of the more ancient formations, so far 

 as they are known, teach us little concerning the stages of 



