MEGA THER1ID& 



unlike the true canines of heterodont mammals. Vertebrae : C 6 

 or 7, D 2 3-24, L 3, S 7-8, C 4-6. One species (C. didactylus) has 

 the ordinary number of vertebrae in the neck ; but an otherwise 

 closely allied form (C. hoffmanni) has but six. The tail is very 

 rudimentary. The hand generally resembles that of Bradypus ; but 

 there are only two functional digits with claws those answering 

 to the second and third of the typical pentadactylate manus. The 

 structure of the hind limb generally resembles that of Bradypus, 

 the appellation "two-toed" referring only to the anterior limb, 

 for in the foot the 

 three middle toes 

 are functionally 

 developed and of 

 nearly equal size. 

 C. didadylus,vf}iich 

 has been longest 

 known, is com- 

 monly called by 

 the native name 

 of Unau. It in- 

 habits the forests 

 of Brazil. C. hoff- 

 manni (Fig. 58) 

 has a more north- 

 ern geographical 

 range, extending 

 from Ecuador through Panama to Costa Rica. Its voice, which 

 is seldom heard, is like the bleat of a sheep, and if the animal is 

 seized it snorts violently. Both species are very variable in 

 external coloration. 



Nothropus. 1 The only fossil form which has been referred to 

 this family is indicated by a lower jaw, described by Dr. Burmeister, 

 from the Pleistocene of Argentina, which appears to have belonged 

 to an animal of about double the dimensions of Choloepus didactylus. 

 Professor Cope states, however, that this jaw really belongs to a 

 Glyptodont; while it is referred by Dr. Ameghino to the next 

 family. 



Family MEGATHERIID^E. 



The members of this family are all extinct. Their characters, 

 so far as is known from the well-preserved remains of many species 

 found abundantly in deposits of Pleistocene age in both North and 

 South America, were intermediate between those of the existing 

 Bradypodidce and the Myrmecophagidce, combining the head and 

 1 Burmeister, Sitzb. Ak. Berlin, vol. xxviii. p. 613 (1882). 



FIG. 59. Skull of Two-toed Sloth (Cholcepus didactylus). From 

 Proc. Zool. Soc. 1871, p. 432. 



