8 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



ing each several species. The discovery of more complete material may 

 reduce these numbers, but the variety will continue to be remarkable. 



Attention has already been called to the difference between the Santa 

 Cruz and the recent armadillos, a difference which can be made clear in a 

 few words. No probable forerunner of Dasypus, Priodoiites, Tolypeiites, 

 CJilamydoplionis, or Tatu, has been found in these beds, though some one 

 of the species of Prozaedius was almost certainly an ancestor: of the recent 

 Zacdyus, and it is possible, though far from certain, that some species of 

 Stenotatns stood in the same relation to the modern Cabassous. In view 

 of the stage of differentiation attained by the Santa Cruz armadillos, it is 

 most improbable that all of these modern types should have originated 

 since that period. This confirms the conclusion indicated by several 

 other mammalian series, that in Miocene times Patagonia was not the 

 principal theatre of evolution of the South American fauna. This would 

 explain the entire absence from the Santa Cruz beds of many types which 

 would naturally be expected to occur there. 



In general, the armadillos of this period may be said to have attained 

 nearly the modern degree of specialization, though, in many details, prim- 

 itive characteristics have been retained. As Ameghino has pointed out, 

 ('94, 178) the carapace never has an anterior buckler, but is made up of 

 movable, imbricating bands, except posteriorly, where a larger or smaller 

 number of plates are joined together by their edges to make the pelvic 

 buckler. In one genus, Prcetiphractus, (fide Ameghino) there is no pelvic 

 buckler, all the plates being movable, and it is uncertain whether this was 

 not also true of Stegotherium. In Peltephilus the pelvic buckler would 

 appear to have been very loosely formed, the plates merely touching one 

 another, though in this region they are not imbricating. The cephalic 

 shield is usually composed of numerous small, non-imbricating, irregu- 

 larly polygonal and rather heavy plates, which are finely pitted and dis- 

 play no regular sculptural pattern, but in the altogether exceptional 

 genus Peltephilus these plates are large, very thick and coarsely sculp- 

 tured. A further remarkable peculiarity of the head-shield in this genus 

 is the presence of one or two pairs of pointed, horn-Jike scutes upon the 

 rostrum. It is a curious fact that no plates of the tail-sheath have been 

 found in association with any of the genera, except Peltephilus. It seems 

 most 'unlikely that all the other genera had unarmored tails and yet, in 

 view of the large number of well-preserved specimens, including the 



