NORTH AMERICA AND THE WEST INDIES 37 



incisors and canines of the lower series are also lacking. The 

 skull is relatively long and narrow instead of globular as it is in 

 the tree-living types, the rostrum is short and broad, and there 

 is a well-developed median crest extending forward from the 

 wide occipital ridge to the frontal region, where a lower branch 

 goes to each of the short postorbital projections. The large 

 tusklike upper canines are strongly triangular in section, 

 followed by a diastema of nearly the same length as the diam- 

 eter of the tooth or somewhat longer, then four cheek teeth in 

 two parallel rows, each tooth approximately oval in section, 

 with the broader end on the lingual side. In the lower jaw, 

 there is a large tusklike first premolar corresponding to the 

 upper canine, then a space, followed by three cheek teeth 

 much like those of the upper series. The humerus has a 

 slender shaft, a wide distal expansion, and a large entepicondy- 

 lar foramen. The femur is wide in front view, but not thick, 

 and shows a low third or outer trochanteric ridge. The tibia is 

 short and stout and the fibula is free. The calcaneum or heel 

 bone is broadly hatchet-shaped, and the terminal phalanges 

 were evidently provided with stout claws. The tail is believed 

 to have been short but rather stout. Dr. Anthony gives the 

 following dimensions of the major skeletal elements: Skull 

 length, tip of rostrum to occipital condyles, 136.2 mm.; breadth 

 of brain case, 28.5; greatest breadth across postorbital proc- 

 esses, 47.5; alveolar length of upper molar series, 35.5; longest 

 humerus, 145; ulna, 160; radius, 128.8; longest femur, 163.3; 

 longest tibia, 128. 



Among the remains of this species recovered in caves in 

 Puerto Rico were a few indicating a similar sloth of slightly 

 larger size, which Dr. Anthony in a later communication 

 decided must represent a second and larger species of the same 

 genus. This he named Acratocnus major, and defined it as 

 being very similar to A. odontrigonus but "larger and heavier 

 and with different skull characters"; it has "proportionally a 

 much broader muzzle and an elevated basioccipital region," 

 and a larger upper canine. No complete measurements of the 

 skull are available, but the breadth across postorbital processes 

 is 66 mm.; length of ulna, 171; length of tibia, 133. By com- 

 parison with the corresponding measurements given above for 

 the smaller species, the obvious size difference may be appre- 

 ciated. 



