CHARACTERS OF SOME HYSTRICOMORPH RODENTS. 395 



more symmetrically ai'tiodactyl. The plantar pad is wider as 

 compared with its length than in Coelogenys, and its three com- 

 ponent elements are less well defined than even in that genus, 

 and markedly less so than in Chinchilla. As in Chinchilla, the 

 carpal pad is larger than the plantar pad and closer to it than 

 in Coilogenys, but it is not so distinctly divided into two as in 

 those genera, and, as in Chinchilla, the outer side of the wrist is 

 normally hairy. 



The hind foot differs from th.at of Chinchilla and Ccdogenys in tlie 

 complete suppression of the fifth digit and of the corresponding 

 element of the plantai' pad. The second digit, moreover, is very 

 markedly shorter than the fourth *, and the latter, too, although 

 long, is shorter in comparison with the long third digit than in 

 Chinchilla and Ccdogenys. The claws of these thi-ee digits are as 

 powerful relatively as in Ccdogenys. The plantar pad, as in those 

 genera, is composed of two elements, but they are very indistinctly 

 defined, and the whole pad is three-lobed with emarginate 

 antero-lateral and posterior borders. The metatarsal pad is large 

 and horny, but undivided. A peculiarity of the foot is the 

 encroachment of the hairs of the outer side nearly up to the 

 middle line, overlapping, with those of the opposite side, the 

 area between the plantar and metatarsal pads ; and a further 

 difierence from Chinchilla is the development of a thick bunch 

 of stiff" bristles on the inner side of the third digit. Chinchilla 

 has long hair in this position, but the brush, or comb, is 

 specially developed upon the second digit. The feet of this genus 

 are interesting, because they connect those of the Chinchilline 

 with those of the typical Caviine section of the group of Rodents. 

 The hind foot is also modified on much the same lines as tha,t of 

 Dasyprocta, although the fore foot is very different. (Text- 

 fig. 14, C, D.) 



The feet of Cavia porcellus, the domesticated Guinea-pig, have 

 been figured and described by Mivart and Murie (P. Z. S. 1866, 

 pp. 383-417), and by TuUberg. In the artiodactyle fore foot the 

 pollex is suppressed and the four remaining digits are moderately 

 long and subsymmetrically arranged, the third and fourth being 

 subequal and longer than the second and fifth, which are also 

 subequal. The claws project well beyond the normally shaped 

 digital pads. The plantar pad is well defined and three-lobed, 

 the median lobe being the largest. Behind the plantar pad 

 there is a single carpal pad, separated from it by an area of 

 naked skin. The hind foot is perissodactyle, with only three 

 toes, whereof the median (the third) is the longest. The claws 

 are longer than in the fore foot. The plantar pad is moderately 

 well defined and two-lobed, the inner lobe being much smaller 

 than the outer. The metatarsal area has no large horny plate 

 representing the pads, which are merely indicated by a single 



* It must be remembered that the numerical terms apph'ed to the digits through- 

 out this paper are used in a homologica! sense, as if the limbs were normally 

 pentadactj'le. 



