EDENTATA OF THE SANTA CRUZ BEDS. 125 



thickened at the free end ; the transverse processes are long and heavy 

 and bear large facets for the tubercles of the ribs. In the dorsal tube, 

 which has a longitudinal curvature, the centra are longer, narrower and 

 thicker, increasing in size posteriorly, with kidney-shaped, slightly opis- 

 thocoelous faces ; in the anterior part of the tube the neural canal is very 

 small, but enlarges much posteriorly ; the coalesced neural spines form a 

 prominent and continuous ridge, with thin free border, while in the Pam- 

 pean genera this border is very thick ; another difference from the latter 

 is in the separateness of the transverse processes, which are much elevated 

 and thickened at the distal end and are connected only by a very thin 

 ridge of bone which runs along their mesial sides. 



The lumbars are seven or eight, the first of which forms part of the 

 dorsal tube, while the others have united together and with the sacrum to 

 form a second tube (Plate XXV, fig. 3) ; between the two is a movable 

 joint, the first lumbar with post-zygapophyses and the second with prezyga- 

 pophyses, both well developed, and, it is especially interesting to note, a 

 pair of accessory articular processes. The centra of the lumbar vertebrae 

 become larger, but more depressed, and the neural canal enlarges pos- 

 teriorly ; on the last three is a pair of prominent and parallel ventro- 

 lateral keels ; the metapophyses, when present, are high and thin, but they 

 are absent from the last three lumbars ; the neural spines form a high, 

 thin ridge, which rises far above the level of that of the dorsal tube ; trans- 

 verse processes are lacking. 



The sacrum is composed of seven or eight vertebrae, of which the 

 anterior two are connected with the ilia ; the coalesced centra form an 

 arched, slender, almost rod-like body, though the last one is much thick- 

 ened for the attachment of the heavy tail ; transverse processes are obso- 

 lete on most of the sacral vertebrae, but on the last two or three they are 

 very long, broad and plate-like, and their distal ends are fused with the 

 ischia. The fused neural spines of the sacrum form a high, thin and 

 arched crest and are continuous with the similar crest of the lumbars ; 

 large postzygapophyses are present on the last vertebra. 



The caudal vertebrae (Plate XXV, figs. 4-10) probably did not exceed 

 twelve or thirteen in number ; in the La Plata skeleton eleven are pre- 

 served in continuous series and apparently only the terminal one is miss- 

 ing. In its proportions the tail resembles that of Glyptodon rather than 

 that of the other Pampean genera, being short and massive and tapering 



