CHARACTERS OP SOME HYSTRICOMORPH RODENTS. 403 



the space between the third and fourth, and the outer smaller, 

 rounder, and set further back behind the base of the fifth. The 

 metatarsal area is mostly covered with a smooth horny plate, with 

 bilobed aiiteiior border separated from the plantar pad by a 

 shortish naked area of skin. (Text-fig. 19, D.) 



The fore foot of Gtenodactylus yundi has only four tolerably 

 long and slender digits, which are subequal in length, sub- 

 equally spaced, and widely separable. The pollex is absent. The 

 skin of the louer side of the digits is smooth, the digital pads 

 are well developed, and marked in their posterior half by two 

 transverse grooves. The claws are short, sharp, and curved. 

 The plantar pad is very large, markedly three-lobed, and very 

 coarsely areolate. Immediately behind it there are two large 

 smooth carpal pads in contact in the middle line, or nearly so, 

 each longer than wide and the two together as wide as the 

 plantar pad. (Text-fig. 18, A.) 



The hind foot has digits similar in number and shape to those 

 of the fore foot, except that they are relatively much longer with 

 reference to the plantar pad, which is in a general way like that 

 of the fore foot in shape and sculptm-ing. The claws are short, 

 sharp, and curved ; and the two inner digits, the 2nd and 3rd, 

 are provided with combs of bristles similar to those of Ctenomys, 

 but there are three of them on each digit instead of two. The 

 tips of the remaining digits also have long bristles, but these are 

 much thinner than those of digits 2 and 3. There are two 

 elongated smooth metatarsal pads, separated by a definite area of 

 transversely wrinkled skin from the plantar pad. They are in 

 contact throughout their length, and the outer of the two 

 extends back to the heel. (Text-fig. 18, B, C.) 



Genital Organs of the Male. 



A peculiarity of the penis of the Hystricomorphs is the 

 pi-esence at tlie tip of the gland, behind and below the orifice, of 

 a wide slit leading into a sac, with laminated or corrugated walls, 

 which can be evaginated and withdrawn again by the action of a 

 pair of tendons. In some genera, as recorded below, this sac 

 is provided with a pair of horny spikes arising from its floor, as 

 was recorded long ago in the case of Cavia, Cmlogenys, and Dasy- 

 procta. Tullberg's conclusion as to the generic incidence of 

 these spikes does not tally at all with mine. He says they are 

 distinctive of the family Oaviida?, which for him included the 

 genei-a Dasyprocta^ Codogenys, Cavia, Dolichotis, and HydroGhce,rus. 

 He does not, however, appear to have seen the penis of Dolichotis. 

 Hence his generalization with respect to it must have been 

 merely inferential. The spikes were not present in the example 

 of Dolichotis examined by me ; they were also absent in two 

 specimens of Hydrochoirus, although, according to Tullberg, the 

 penis of this animal resembles that of Cavia in essentials. I 

 have also found these spikes well developed in genera. which fall 



