EDENTATA OF THE SANTA CRUZ BEDS. 12J 



The ribs are already characteristically glyptodont ; the first rib is short, 

 broad and plate-like, presenting directly forward and with distal end fused 

 with the presternum. The succeeding ribs are broad, but very thin and 

 laterally compressed ; the proximal end forms a hammer-shaped expansion 

 which, at least in the anterior part of the thorax, bears three distinct facets 

 for the vertebrae. The sternal ribs are stout and articulate with the verte- 

 bral ribs by well-developed synovial joints ; in relative size and shape 

 they strikingly resemble those of the armadillo Proeutatus. 



Of the sternum, the La Plata skeleton retains the manubrium, the last 

 segment of the mesosternum and the xiphisternum. The manubrium is 

 short, very broad and thin, and its lateral borders are fused with the first 

 pair of ribs ; the anterior margin is somewhat concave, with a pair of prom- 

 inent tubercles, which seem to indicate the presence of clavicles, though 

 none have yet been found in association with any of the specimens. The 

 last segment of the mesosternum is short and thick and has two pairs of 

 concave facets for the sternal ribs. The xiphisternum is very long, de- 

 pressed and thin, quite broad anteriorly, but tapering behind to a blunt 

 and slightly upcurved point. 



Appendicular Skeleton. To a certain extent, the limbs of the genus 

 are intermediate in character between those of the armadillos and those 

 of the Pampean glyptodonts, and though decidedly nearer to the latter, 

 are yet much less massive. The fore-limb is considerably shorter than the 

 hind, the relative lengths of the two pairs being almost exactly as in Glyp- 

 todon. 



The scapula (Plate XXVI, fig. i) differs from that of the Pampean 

 genera in its narrowness and consequent resemblance to that of such an 

 armadillo as Proeutatus ; the glenoid cavity is elongate antero-posteriorly, 

 narrow transversely ; the neck is very broad and the coraco-scapular notch 

 hardly indicated ; the pre- and postscapular fossae are of nearly equal size, 

 but of different shape, and the postero-superior angle of the blade is more 

 like that of Glyptodon than the slender, sickle-shaped process seen in 

 Sclerocalyptus ; the spine is very prominent and its free border is very 

 wide and recurved, much more like that of Proeutatiis than that of the Pam- 

 pean genera ; the acromion is long and incurved and there is a large meta- 

 cromion ; the posterior spine-like ridge is distinct from the glenoid border 

 and much more prominent than in the later glyptodonts. The coracoid is 

 large, thickened at the end and indistinguishably fused with the scapula. 



