CHARACTERS OF SOME HYSTRICOMORPII RODENTS. 383 



edge of the cavity. The edge or rim is raised all round, defining 

 a de^p hollow divided into two by a large valvular siipratragus, 

 which separates the upper third from the lower two-thirds of the 

 cavity. There is no tragus ; but the antitragus forms a long, 

 narrow, infolded, naked ridge, from the upper end of which a 

 short ridge i-uns obliquely forwards, upwards, and inwards to 

 terminate in the middle of the cavity beneath the supratragus. 

 A corresponding ridge occupies a similar position in the anterior 

 half of the lower two-thirds of the cavity. The orifice of the 

 auditory meatus is a large hole situated just within the lower 

 half of the antitragal ridge. (Text-fig. 6, N.) 



According to Dobson, the ear of Pectinator resembles that of 

 Ctenoclaciylus except that it i-etains the antitragal thickening 

 which the latter, he alleges, has lost. Since, however, thei'e is a 

 long low antitragus in the examples of Ctenodactijlus I examined, 

 this distinction does not hold. Dobson probably overlooked this 

 structure in Ctenodactiilus owing to its being normally folded 

 inwards. Assuming that their ears are similai', these two 

 genera differ markedly not only from all the Hystricomorphs, 

 but from all other Rodents kno^vn to me in the structure of 

 this organ. 



The Feet. 



In Hystrix, Acanthion, and Atherura the fore foot is short and 

 broad. The four main digits are short, subequal, moderately widely 

 separable, and united by naked integument up to the proximal end 

 of the large smooth digital pads. The claws are tolerably long, 

 strong, and fossorial. The pollex, on the other hand, is greatly 

 I'educed and represented externally merely by its nail and small 

 pad. It arises alongside the outer distal extremity of the radial or 

 inner carpal pad, behind or abos^e the inner lobe of the plantar 

 pad. The plantar pad is smooth, about twice as wide as long, and 

 three-lobed. The median lobe projects in the middle line and 

 is larger than the lateral lobes, of which the inner is smaller 

 than tlie outer. The posterior border of the pad is almost 

 sti'aight from side to side. Immediately behind it ai-e two large 

 smooth carpal pads, separated by a naked space, or nearly in 

 contact, and behind the pads there is a short area of naked skin 

 overlapped by the bristly hairs above it. 



The digits and plantar pad of the hind foot are, in general 

 features, tolerably similar to those of the fore foot, except that 

 the hallux is better developed than the pollex and arises just in 

 front of the inner lateral lobe of the plantar pad. The sole of 

 the foot behind the plantar pad is smooth and naked back to the 

 heel, and is occupied for the most part by two large, but not well- 

 defined, metatarsal pads. (Text-fig. 8 ) 



The feet of Dinomys^ judging from the description and figures 

 published by Peters *, appear to be moi^e like, those of Ilystrix 



* Fostschv. Ges. Nat. Berlin, 1873, p. 228, pi. iii. figs. 2, 3. 



26* 



