CHARACTERS OF SOME HTSTRICOMORPH RODENTS. 397 



approximately equalling the plantar pad in size. On the inner 

 side of the fore foot there is an area covered Avith short hairs, 

 as in Dasiiprocta and Coilogenys. In the hind foot the gi'eater 

 part of the metatar.sal area is covered with a large horny shield, 

 like that of Dasyfrocta. (Text-fig. 15, A, B.) 



In DoUchotis patagonica the fore foot is symmetrically artio- 

 dactyle, the second and third digits being subequal and longer 

 than the fourth and fifth, which are likewise subeqnal. The 

 pollex is absent. The claws are modeiately long but bhmt, and 

 the digital pads are very well defined. The plantar pad is a 

 large, thick, irregularis' hexagonal cushion set far forwards 

 beneath the digits. Its edges are emarginate opposite the inter- 

 digital spaces, and its posterior border is mesially notched. It 

 is exceedingly deep, and the gait of this genus is markedly 

 digitigi-ade. The metacarpal area behind the plantar pad is 

 remarkably long, and there is a single very small carpal pad 

 remote from the plantar pad. TTie hind foot, as in Cav^ia, 

 Dasyprocta, and Hydrochcerus, is perissodactyle and furnished with 

 three digits, which resemble those of the fore foot in essential 

 particulars. The plantar pad is relatively as large and high as 

 in the fore foot, but differently shaped ; its edges are more 

 evenly convex, and there is a single median prccess in front 

 corresponding to the median or thii'd digit. It is composed of 

 two indistinctly defined elements. This foot, like the fore foot, 

 is markedly digitigrade, the posterior portion of the plantar pad 

 projecting like a heel. The metatarsal area is very long, and 

 its posterior half is covered with a single horny shield, upon 

 which the animal squats, like Hydrochcerus. Dasyprocta. Kerodon, 

 and others. In both the fore and the hind foot the naked lower 

 side of the digits and of the area behind the plantar pads is 

 overlapped by the hairs of the sides of those parts. (Text-fig. 16.) 



DoUchotis scdinicola has feet closely resembling those of pata- 

 gonica, except that, judging from the single example examined, 

 the metacarpal area of the fore foot is shorter and the carpal 

 pad a little larger and closer to the plantar pad. 



If the habits of DoUchotis were unknown, it would not be 

 diflicult to infer from the structure of its feet that the animal 

 is adapted for swift running over hard ground. The differences 

 the feet present from those of Caria may be ascribed to adapta- 

 tion to that mode of life. 



The feet of Hydrochcerus difl:er in several important respects 

 from those of Cavia. This is particitlarly the case with the 

 fore foot, which, as in Cavia, has no pollex, but is perissodactyle, 

 the third digit being the largest and situated in the middle line, 

 with the second and fourth, which are subequal, flanking it 

 laterally ; and these three digits are united by narrow webbing 

 up to the digital pads. The latter, however, are scarcely recog- 

 nisable as such, being represented by a softish thickening of 

 integument blending without line of demarcation with the skin 

 of the dicrit behind and with the claw in front and forming a 



Proc. Zool. Soc— 1922. Xo. XXTII. 27 



