CHARACTERS OF SOMIi II VSTRICOMORPH RODENTS. 385 



siibequal, 2 being set a little more foi-vvanls than 5. The inter- 

 digital webbing, however, does not perhaps extend so far distally 

 as in Hystrix, and the soles are — in part, at all events — covered 

 with squaniiform papillae instead of being smooth. The plantar 

 pad of the fore foot seems to be of much the same form as in 

 Hjjstriv, and just behind it and in contact with i't there is an 

 immense carpal pad with a median depression indicating its 

 division into the two normal elements. The plantar pad of the 

 hind foot is reduced to three smooth isolated prominences rising 

 from the papillate integument ; and the metatarsal area shows no 

 trace of the two pads, but is uniformly papillate in its distal 

 portion, where it is scarcely defined from the plantar portion, 

 and smooth and swollen in its proximal portion up to the heel. 

 (Text-fig. 19, A, B, p. 402. > 



In Octodon degas the fore foot is artiodactyle, the third and 

 fourth digits being paired and subequal and a little longer than 

 the second and fifth, which are also subequal, the fifth, however, 

 being a little the shorter of the two. These four digits ai'e stout, 

 shortish, with sharp moderateh^ long claws; the pollex is quite 

 short and i-epi-esented externally by little more than its claw. 

 The plantar pad is large, as wide as the foot, considerably wider 

 than long and markedly three-lobed, the median lobe being larger 

 than either of the others. It is covered with papillae, which 

 spread on to the base of the digits, and each lobe is provided with 

 a single large papilla opposite the three interdigital spaces. The 

 double carpal pad of which the two elements ai'e mesially in con- 

 tact, the outer being a little the larger, is a little larger than the 

 plantar pad and, like it, covered with papillae, with a single 

 enlarged papilla at the antero-external corner of each. Behind 

 this pad there is a naked triangular area of skin. (Text-fig. 9, B.) 



In general features the hind foot is like the fore foot, but the 

 digits ai-e much longer and the plantar pad narrower and the 

 hallux is relativ^ely much longer than the pollex. There is a, 

 single enlarged circular papilla opposite the four interdigital 

 spaces, and two others on the metatarsal area, one set forwards 

 on the ulnar side just behind the outer moiety of the plantar pad 

 and the other farther back on the radial side some distance 

 behind the papilla opposite the space in front of the hallux. Th.e 

 whole plaiita.r surface is covei'ed with small papillae, except the 

 heel, which is naked ; and there is a median groove defining the 

 two elements of the metatarsal pads. I regard the feet of 

 Octodon as the most generalised type found in the Hystricoraorph 

 Rodents. (Text-fig.''9, A.) 



Winges figures of the feet of sevei'al genera of Lonchei'inae 

 {LoncJieres, Echimys, Trichomys (jYelomys), Carterodon, Mesomys) 

 show that, with variations in detail, they conform tolerably closely 

 with those of Octodon degios. They are pentadactyle with greatly 

 reduced pollex and short hallux ; the primary interdigital ele- 

 ments of the plantar pads are separated, but they are rela- 

 tively much larger than in Octodon, and the papillate areas of 



