434 DR. J. E. GRAY ON THE BRADYPODID/E. [May 2, 



near the internal nostrils, in the other the groove is narrow and the 

 opening of the internal nostrils much more constricted ; but one of 

 the skulls with the arched forehead (1510 e), received from Capt. 

 Kellett, has the grooves of the pterygoids much wider than in the 

 others, and rather contracted instead of dilated in front at the open- 

 ing of the nostrils. 



a. Crown flattened, broad. Brady pus didactylus, Blaiuville's 

 Osteog. t. iii. fig. (skull, adult and young). 



Skull (736 a), adult. Columbia. 



Skull (7366), young. B. didactylus, Rapp, Edentata, t. iii. 

 fig. 2, 3. 



Skull with the nose very deformed. Choloepus hoffmanni. Ve- 

 ragua. 



b. Crown arched longitudinally and transversely. 

 Skull adult (736 d). Ecuador. 



Skull adult (151 Oe). Choloepus hoffmanni, Capt. Kellett, is pe- 

 culiar for having the nasal bone prominent beyond the edge of the 

 nose and thoroughly anchylosed to the other bones. 



c. Skull very young. Nose only preserved, narrower than the 

 rest. No. 736c. 



The skull from the very adult skeleton (15106) appears to belong 

 to this variety ; but the flatness of the hinder part of the crown 

 renders it intermediate between the two. It has a very broad canal 

 between the pterygoids, like the skeleton (1510e); and the ptery- 

 goids of these two skulls are not nearly so vesicular as in the other 

 specimens. 



d. There are three skulls of young animals, one received from 

 Dr. Peters from Costa Rica as Choloepus hoffmanni, and two received' 

 from Costa Rica by Mr. Salvin. 



They are all peculiar for having the scars of the temporal occupy- 

 ing the whole of the hinder part of the skull, and only separated 

 from each other by a narrow ridge. The oldest of the three (15 lOe) 

 has a rounded convex forehead and a narrow groove between the 

 pterygoids, which are dilated in front, and a small distinct nasal. 

 The next in age (1510a), received from Dr. Peters, has a broad more 

 flattened forehead; and the smaller one, from Mr. Salvin (lo\0d), 

 has a still more flattened forehead ; these two have a very broad 

 groove between the pterygoids, narrowed in front ; in fact the skulls 

 of the species of Choloepus are exceedingly variable in external cha- 

 racters in specimens from the same locality. 



Tribe II. Bradypodina. 



Hands and feet three-clawed. Skull oblong. Front end of the 

 lower jaw truncated, without any or only a very short anterior spoon- 

 like lobe. Intermaxillaries rhombic, rudimentary, not united to the 

 front of the maxilla, generally lost in maceration. The front upper 

 grinders small, cylindrical, truncated, not nearly so large as the 

 others. The second upper grinder largest, generally gradually 

 smaller backwards. The front lower grinder broad, compressed, 



