XEXARTHRA. 545 



C9, D15-17, Lo-3, SO, Cll ; manus and pes with 3 digits (2, 3, and 4) ; 

 with trapezoid and os magnum united ; 2 pectoral mammae ; trachea 

 folded on itself ; several species, but number uncertain, Guiana, Brazil, 

 Peru, Isthmus of Panama. Choloepus 111., two-toed sloths ; anterior 

 tooth in each jaw caniniform and separated by diastema from the others ; 

 vertebrae C6 or 7, D23-24, L3, S7 or 8, C4-6 ; manus with 2 digits 

 (2 and 3), pes with 3 digits (2, 3, 4) ; 2 species ; Ch. didactylus L., unau. 

 Extinct genera are Entelops and Trematherium Amegh., Eocene of Pata- 

 gonia. 



A number of extinct families, intermediate between the sloths and 

 anteaters, are united Tinder the heading of Gravigrada (ground -sloths). 

 They are for the most part of considerable size, and are found in the 

 Tertiaries of N. and S. America. They date from the Eocene. In their 

 skull and dentition they resemble the sloths, in the vertebral column, 

 limbs and tail the anteaters. The teeth are usually f , and consist of 

 dentine and cement. The anterior border of the scapula is joined to the 

 coracoid process as in the two preceding families, and there is a well- 

 developed clavicle. In some, small bony nodules were present in the 

 skin. The jugal is very strong and has a downwardly directed process. 

 Tail well developed. 



Fam. 3. Megatheriidae. With very deeply-rooted prismatic teeth, 

 quadrate in section and set in close 

 series. Megatherium Cuv., enormous 

 animals with a small head, a body 

 as large as that of an elephant but 

 with shorter limbs ; skull sloth-like, 

 zygoma complete with descending 

 process ; complete skeletons are 

 known ; Pleistocene of S. and C. 

 Amer. and of the southern United 

 States. Inter -odon Amegh., Oligo- 

 cene, Pliocene of Argentina ; 

 Promegatherium Amegh., Oligocene, 



Argentina, with bands of enamel on FlG - 284. Skull of Bradypus torquatus 



(from Claus). 

 the teeth ; and other genera. 



Fam. 4. Mylodontidae. With prismatic teeth, sloth-like skull, and 

 jugal reaching back to squamosal but not united to it ; skin often with 

 ossifications. Mylodon Owen, as large as a rhinoceros, dermal bony 

 plates not fused together ; Pliocene and Pleistocene of S. Amer. and 

 United States. Glossotherium Ow., Pliocene and Pleistocene of Argen- 

 tina. A portion of the skin of this animal with the hair perfectly pre- 

 served was discovered by Moreno in Patagonia in 1897 (Proc. Zool. Soc. 

 1899). A number of scattered small ossicles were embedded in it, and it 

 was assigned to a new genus Neomylodon. Later another piece of skin 

 was found by Hauthal in a cave in S. Patagonia in association with some 

 bones of an extinct ground sloth which has since been identified as Glosso- 

 therium (Grypotherium) (Proc. Zool. Soc., 1900, p. 64). A quantity of 

 cut hay and a thick deposit of the excrement of a large herbivore, pre- 

 sumably Glossotherium, were also found in the cavern, and Hauthal formed 

 the conclusion that the animal had been kept and fed by man. The 

 bones are in a very fresh state of preservation, retaining their gelatine 

 and showing traces of the dried periosteum and ligaments. There can be 

 little doubt that the skin and bones belonged to the same species of animal 



z ii. N N 



