Dkoembeb 21, 1900.] 



SCIENCE. 



939 



extraordinarily interesting and curious ex- 

 tinct lines. Ameghino has already called 

 attention to some of the peculiarities of 

 these Santa Cruz Armadillos, such as the 

 movable arrangement of the bony scutes of 

 the carapace, which do not form a fixed 

 shoulder-shield, and the imbricatin , over- 

 lapping disposal of the scutes in several of 

 the species. As yet no member of the Ant- 

 eaters or true Sloths has been detected in 

 the collection, and it is still too early to say 

 whether this absence is due to the accidents 

 of foBsilization and of collecting, to geo- 

 graphical and climatic factors, or to the 

 fact that these families had not yet become 

 distinctly separated from the others. 



Even more surprisingly abundant and 

 varied are the Rodentia, of which a remark- 

 able number of genera and species may be 

 distinguished. These are, without one cer- 

 tainly known exception, members of the 

 Hyslricomorpha and are all closely allied 

 to types which continue to flourish in South 

 America at the present time. Indeed, sev- 

 eral of the fossils cannot be generically 

 separated from living forms. In all this 

 great assemblage of rodents are to be found 

 no beavers, marmots or squirrels, no rats 

 or mice, no hares, rabbits or pikas, but only 

 a bewildering variety of cavies, pacas, chin- 

 chillas, agoutis and the like. In no mam- 

 malian order are the isolation of the Santa 

 Cruz fauna and its separateness from that 

 of the northern hemisphere more clearly 

 displayed than in the Eodentia. 



Still more peculiar are the hoofed-ani- 

 mals. The four orders into which this 

 great series is divided in the table do not 

 represent the results of mature study, but 

 merely of a preliminary survey of the ma- 

 terial, and the number of ordinal groups is 

 subject to increase or diminution, as may 

 be the outcome of more careful examina- 

 tion. Of the four orders not one is known 

 in the Miocene of the northern hemisphere, 

 nor, on the other hand, does the Santa Cruz 



contain representatives of any ungulate 

 order common to it and the northern con- 

 tinents. All the four orders, except the 

 As trapotheria, continue into the Pleisto- 

 cene, when most of them had become beasts 

 of great stature or bulk; but then they all 

 disappeared completely and have left no 

 descendants in the modern world. 



The Typotheria are individually much 

 the most numerous of the Santa Cruz un- 

 gulates and they are, within certain narrow 

 limits, extraordinarily varied. They are 

 all small animals, some of them very small, 

 and except for their long tails, of an aspect 

 which strongly suggests relationship with 

 the Hyracoidea. Whether this resem- 

 blance is anything more than an analogy, 

 remains to be determined by a series of 

 careful comparisons. This phylum termi- 

 nates in the rodent-like Typotherium of the 

 Pleistocene, an animal which, though only 

 of moderate size, is yet very much larger 

 than any of its Santa Cruz predecessors. 

 The order has not been found outside of 

 South America. 



The next most abundant of the Santa 

 Cruz ungulates is the order Toxodontia, 

 which is very much less varied than the 

 preceding group, though its members are 

 much larger ih size. These relatively 

 massive, short-legged and short-footed ani- 

 mals are remarkable for the great size of 

 their heads and for their curved, per- 

 sistently growing teeth. This line also ter- 

 minates in the Pleistocene in the great 

 Toxodon, which ranged as far north as 

 Nicaragua. The supposed representatives 

 of the order which have been reported from 

 Europe are simply mistakes of identifica- 

 tion. 



Most remarkable and interesting of all 

 the Santa Cruz ungulates are the Litopterna, 

 which in many respects closely parallel the 

 Perissodactyla. Of these there are two 

 series, one of long-legged, long-necked, 

 camel-like animals, which led up to the 



