EDENTATA OF THE SANTA CRUZ BEDS. 1 07 



GLYPTODONTIA. 



The Santa Cruz glyptodonts have already attained a high degree of 

 specialization, but they are in many respects distinctly more primitive 

 than those of the Pampean and were obviously converging to a common 

 ancestry with the armadillos. So far as the available material enables 

 us to judge, there is comparatively little variety among them, the differ- 

 ences between the five genera that have been described being of a very- 

 subordinate kind, and none of them is known to persist to a later epoch. 



1. The most striking distinction between these genera and those of 

 later times is in size ; the Santa Cruz species are all small, some of them 

 very small, and only those of a single genus, Eucinepeltus, approximate 

 the lesser Pampean species in stature. 



2. In all cases the carapace is made up of transverse bands or rows 

 of plates, which doubtless permitted a certain degree of flexibility, as is 

 shown by the fact that on the sides of the carapace, near the anterior 

 end, are two or three rows of overlapping, imbricating plates, like those 

 of the armadillos. There is, however, a surprising amount of variability 

 in the number of these movable bands, even on the two sides of the same 

 individual. It is unusual to find any of the scutes fused with their 

 neighbors ; I have observed this only in Cochlops and then it consisted 

 merely in the coalescence of two or three adjoining plates. The sculp- 

 tural pattern of the plates is remarkably uniform throughout the genera 

 of the period and agrees closely with that of the Pampean Sclerocalyptns 

 (Hoplophorus], but the plates are relatively thinner and the grooves 

 which make the pattern are shallow. The central figure of each plate is 

 a large oval or, it may be, an obscurely marked polygon, and from its 

 bounding groove radiate a number of short, nearly straight furrows, 

 which demarcate the smaller peripheral figures. The central figure may 

 be plane, slightly concave, or moderately convex, but only in Cochlops 

 has any notable departure from the general plan of ornamentation been 

 observed. In that genus we find on each side of the middle line in the 

 pelvic region, an area in which the pattern of ornamentation characteristic 

 of the remainder of the carapace is extensively modified. In these areas 

 several of the plates display no particular pattern, but merely have a very 

 rough surface, without definite grooves or figures, while in other scutes 

 the central figure is raised into a very high, rugose, bluntly pointed cone, 



