EDENTATA OF THE SANTA CRUZ BEDS. I 1 5 



able, such determination can be made only in the most general terms. 

 Cochlops and Encinepeltus are probably without phylogenetic significance 

 and represent lines that did not persist beyond the Santa Cruz formation. 

 On the other hand, Asterostemma and Propalceohoplophorus are types that, 

 while they may not have actually been ancestral to any of the Pampean 

 genera, are yet not far removed from the common ancestor of them all, 

 and are therefore of great importance. Though still very incompletely 

 known, Metopotoxus would appear to be the forerunner of Panochthus. 



GL YPTODONTID^E. 

 PROPALyEOHOPLOPHORUS Ameghino. 



(Plates XVII; XVIII, XXI, Fig. i ; XXII, XXIII, XXIV, Figs. 1-6, 14; XXV-XXVII.) 



Hoplophorus Moreno, non Lund ; Patagonia, Resto de un antiguo Con- 



tinente hoy Submergido, 1882, p. 26. 

 Propalceohoplophorus Amegh. ; Enumeracion sistem., &c., 1887, p. 24. 



This is by far the most abundant of the Santa Cruz glyptodonts and is, ' 

 for that reason, the most completely known, but much still remains to be 

 learned concerning it, and very extensive additional material will be 

 required before the limits of its surprising variability can be determined. 

 By combining the material in the collection of Dr. Ameghino with that 

 in the museums at La Plata, New York and Princeton, an almost com- 

 plete account of the structure of this genus may be given. 



Exoskeleton. One of the most characteristic features of this genus is 

 the cephalic shield (Plate XXI, fig. i) which differs decidedly from that of 

 any contemporary glyptodont in which the shield is known. The com- 

 ponent plates are all separate from one another and probably numbered 

 28 or 29 ; in the posterior portion they are arranged in three transverse 

 bands, the two hinder bands each of four plates and the third band of 

 three plates ; in the anterior part of the shield are nine or ten smaller 

 plates arranged in longitudinal rows and, finally, over and behind each 

 orbit is a series of four small plates ; much the largest of the plates are 

 the four formed by the median pair of the posterior two bands. The 

 sculpture of the head-shield is essentially like that of the carapace ; there 

 is a large central, more or less convex figure, of irregularly oval or 

 polygonal shape, surrounded by very much smaller polygonal figures, but 

 the bounding grooves are very shallow and consequently the figures are 



