902 



SCIENCE. 



[N. S. Vol. XVII. No. 440. 



that the Gravigrada had already begun to 

 rest the ulnar edge of the hand upon the 

 ground ; the metacarpals are free and, ex- 

 cept in one species of armadillo, none of 

 the phalanges are coossified. The unguals 

 are generally longer and more pointed than 

 in the pes. 



The pelvis differs much in the three 

 groups, but always the ischia are exten- 

 sively connected v?ith the sacrum. The 

 femur is long and has prominent tro- 

 chanters, and in some of the armadillos the 

 great trochanter reaches extraordinary 

 proportions. Tibia and' fibula are free in 

 the Gravigrada, coalesced at both ends in 

 the glyptodonts and armadillos. The pes 

 is pentadaetyl and, except in the glypto- 

 donts, is plantigrade, while in the latter 

 group it is semidigitigrade. No coossifiea- 

 tion occurs in tarsus, metatarsiis or 

 phalanges, and the unguals, which in the 

 ground-sloths are large claws, in the other 

 two orders are more or less hoof -like, com- 

 pletely so in the glyptodonts. 



DASYPODA. 



The Santa Cruz armadillos form a 

 peculiar assemblage of types, very unlike, 

 as a whole, the modern representatives of 

 the suborder, for only one, or possibly two, 

 species would appear to be directly an- 

 cestral to existing forms, while the ma- 

 jority belong to extinct lines. Some of 

 these lines, like that of Proeutatus, for ex- 

 ample, persisted till a much later period 

 than the Santa Cruz, and reached ~ their 

 culmination in the Pampean, but have no 

 representatives in the recent fauna, while 

 other series, like Stegotherium and the ex- 

 traordinary PeltephAlus, are not known to 

 pass beyond the limits of the Santa Cruz 

 formation. At the same time, there is 

 a very notable diversity among these arma- 

 dillos, and no less than three families and 

 seven genera have been described, most of 



the genera having each several species. 

 The discovery of more complete material 

 may reduce these numbers, but the variety 

 will continue to be rem^arkable. 



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 prob- 

 able forerunner of Dasypus, Priodontes, 

 Tolypeutes, Ghalamydophorus or Tatu, has 

 been found in these beds, though some one 

 of the species of Pmaedius was almost 

 certainly an ancestor of the recent Zaedyus 

 —it is possible, though far from certain, 

 that some species of Stenotatus stood in the 

 same relation to the modern Cabassous. 

 In view of the stage of differentiation at- 

 tained 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 indi- 

 cated by several other mammalian series, 

 that in Miocene times Patagonia was not 

 the principal theater of evolution of the 

 South American fauna. This would ex- 

 plain 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, primitive characteristics 

 have been retained. As Ameghino has 

 pointed out, the carapace never has an 

 anterior buckler, but is made up of mov- 

 able, imbricating bands, except posterior- 

 ly, where a larger or smaller number of 

 plates are joined together by their edges 

 to make the pelvic buckler. In one genus, 

 Prceuphractus {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 



