CHARACTERS OF SOME HYSXRICOMORPH RODENTS. 391 



In Ccelogenys tlie fore foot is five-toed and artiodactyle. The 

 pollex is greatly reduced and represented externally merely by 

 its small nail, which is set some distance above the second digit. 

 The third and fourth digits are thick and subequal, and united 

 by webbing halfway between the plantar and digital pads. The 

 second is as thick as the third and considerably shorter ; but it 

 is stouter and longer than the fifth, and set a little more forwards. 

 The web between the second and third and fourth and fiftli is 

 less extensive than that between the third and fourth. These 

 four digits have powerful claws and well-developed smooth pads. 

 The carpal pad is lai'ge, three-lobed, and projects in the middle 

 in front, this portion having a truncated anterior margin. It is 

 roughened with papillae, if not all over, at least in the middle 

 line and laterally at the base of the second and fifth digits. 

 Separated from the plantar pad by a space of naked wrinkled skin 

 are the two well-developed nearly smooth carpal pads which are 

 in contact in the middle line. The whole of the inner side of 

 the wrist as far forward as the base of the second digit is covered 

 with very short hair as in Dasyprocta and Kerodon. (Text- 

 fig. 13, A.) 



The hind foot is also five-toed, but is perissodactyle. The first 

 and fifth digits are short and slender, the first being a little 

 smaller than the fifth ; and they arise nearly opposite one 

 another far up the sides of the foot, only a little in front of the 

 metatarsal j)ads and a long way behind the main mass of the 

 plantar pad. The second, third, and fourth digits are thick and 

 strong, the second and fourth being shorter than the third which 

 lies between them. There is a shallow web between them at the 

 base. The claws and digital pads are similar to those of the fore 

 foot. The main portion of the plantar pad is an irregularly 

 shaped cushion-like mass with two especially strongly papillate 

 areas corresponding to the interdigital spaces and attesting the 

 origin of this pad from two plantar interdigital elements. The 

 remaining two interdigital elements, seen in Octodon, for example, 

 have travelled away from the main portion of the pad, and are 

 represented by small pads at the base of the first and fifth digits, 

 although the one at the base of the first digit (pollex) is not 

 alwaj^s distinguishable. The metatarsal area is covered by a 

 large horny shield, distinctly double at its distal end, but only 

 indistinctly divided in two elsewhere. (Text-fig. 13, B.) 



The feet of Dasyprocta are in many respects very diflerent 

 from those of Ccelogenys, but seem to be derived from that type. 

 They are much thinner and longer. The foi'e foot is perisso- 

 dactyle ; the pollex is even more reduced than in Ccelogenys. The 

 fifth digit also is relatively smaller ; it is, moreover, set high up 

 the foot, almost on a level with the pollex, some distance behind 

 the plantar pad and slightly in advance of the carpal pad. The 

 second, third, and foiu-th digits are well developed, the second is 

 slightly shorter than the fourth, and both a,re shorter than the 

 third which lies between them. There is no visible basal webbing'. 



