EDENTATA OF THE SANTA CRUZ BEDS. 225 



ate thickness ; the neural canal is still quite large and the spine promi- 

 nent and heavy. Passing backward, the successive centra gradually lose 

 the broad, subcubical form and tend to assume a more cylindrical shape ; 

 the neural canal diminishes in size, but is complete to the tenth or 

 eleventh vertebra, and zygapophyses are present on the same number, 

 the anterior pair always much exceeding the posterior in size ; the trans- 

 verse processes grow shorter and relatively wider and are especially 

 expanded at the distal ends, where many of them are more or less dis- 

 tinctly bifid. Near the end of the tail the vertebrae are very small and the 

 processes rudimentary. 



In the anterior and middle regions of the tail the chevron-bones are Y- 

 shaped, as in Megatherium, but with relatively shorter haemal spines ; 

 these spines are longest in the anterior region and diminish posteriorly in 

 length, but retain or even increase their fore-and-after breadth. Proxi- 

 mally, the chevrons bear two pairs of facets for the vertebral centra, of 

 which the anterior pair is larger and persists longer, the posterior pair 

 becoming mere roughened ridges. In the hindermost part of the tail the 

 chevrons are canoe-shaped, very short proximo-distally, elongated antero- 

 posteriorly and pointed at both ends, much as in the armadillos and 

 glyptodonts. 



As a whole, the vertebral column displays an interesting combination of 

 characters ; its nearest resemblance is to the type of the Pleistocene Gravi- 

 grada, but with such differences as might be expected in a more ancient, 

 more primitive and very much smaller and lighter animal, while the very 

 elongate trunk is much like that of Cholczpus. The actual length of the 

 presacral part of the vertebral column is almost the same as in Myrme- 

 cophaga jitbata, but in proportion to the skull and limbs it is far longer, 

 while the tail is much shorter. 



The ribs are incompletely known, but the parts of the thorax are suffi- 

 ciently represented in the various individuals to give a good idea of the 

 whole. The first rib is very short and has a long, straight and very 

 slender neck and a large, saddle-shaped tubercle ; the shaft has its broad 

 side directed forwards and expands distally, where it is fused with the 

 sternal rib. Most of the succeeding ribs are relatively rather short and 

 are strikingly rod-like and slender, forming a decided contrast to those of 

 the larger species, such as H. longiceps ; in the hinder portion of the 

 thorax the tubercles are sessile and obscurely indicated, but apparently 



