EUTHERIA. 691 



related both to the kangaroos and the phalangers. Except the 

 S. American forms already mentioned, Diprotodont marsupials are 

 unknown, either living or fossil, outside the Australian area. Forms 

 related to the Polyprotodonts are, on the other hand, common as fossils 

 in both Europe and America. In S. America, further, fossil mar- 

 supials related to the Dasyuridfe occur ; and as these are not known 

 elsewhere, their presence affords a further confirmation of the view that 

 Australia and Patagonia were once connected. 



/ 



Sub-class Eutheria. Order Edentata. 



This order includes five very distinct families with living 

 representatives — the New World sloths, ant-eaters, and 

 armadillos, the Old World pangolins and aard-varks. These 

 modern forms are specialised survivors of a waning order, 

 and they show many interesting protective peculiarities of 

 structure and habit which secure their persistence. Thus 

 some are arboreal, others are burrowers, and many are 

 covered with strong armature of bone or of horn. 



While the existing sloths, ant-eaters, and armadillos are not nearly 

 related to one another, the numerous fossil Edentates found in S. 

 America connect them to a common stock. It is otherwise, however, 

 with the pangolins and the aard-varks, whose relations to each other 

 and to the other Edentates are exceedingly uncertain. Some authorities 

 separate them (as Nomarthra or Effodientia) from the American 

 Edentates (Xenarthra) ; but according to others there is little evidence 

 that the pangolins and aard-varks are related to each other. In view of 

 the uncertainty, it will be readily understood that few "general 

 characters " of Edentates can be given. Almost the only common char- 

 acters of Edentates concern the dentition. Functional teeth may be 

 absent, but the ant-eaters (Myrmecophagidaa) are the only forms which 

 still appear strictly edentulous. When present, the teeth are uniform, 

 usually simple, without roots, and with persistent pulp. They are 

 never present in the fore part of the mouth, and they have not 

 more than hints of enamel. Till recently the dentition was de- 

 scribed as monophyodont, but there is evidence of two sets in Tatusia, 

 Orycteropus, Dasypus, and others. It is the milk set which dis- 

 appears. 



The placenta shows much variation in character throughout the order, 

 but the reproductive phenomena are somewhat imperfectly known. In 

 the sloths and ant-eaters the placenta is usually described as dome- 

 shaped ; but according to some authorities this is merely a stage in the 

 growth of a placenta, which is at first poly-cotyledonary, and later dis- 

 coidal. The discoidal deciduate type appears again in the armadillos, 

 but in Dasypus among them it is said to be zonary. In the pangolins 

 it is diffuse and indeciduate ; in Orycteropus, apparently by a suppres- 

 sion of the polar villi of a diffuse type, it is zonary, and doubtfully 

 deciduate. 



