CHARACTERS OF SOME HYSTRICOMORPH RODEXTS. 367 



zontidiB {Eretkizoii, Ooenchi, CJmtomys); (7) ^yiitvind^{Hystrix, 

 Atherura, Trichys). 



Of the abov^e-quoted papers TuUberg's is by far the most 

 comprehensive. He dealt as exhaustively as the material at his 

 disposal permitted with the skull, skeleton, and internal anatomy, 

 and, in addition, described and figured the feet of several of the 

 genera, but dismissed very briefly such external organs as the 

 ears and rhinarium. I have been able to supplement his account 

 so far as the organs investigated are concerned, by the exami- 

 nation of some genera he did not see : and in a few particulars 

 connected with the male external genitalia my results diflfer from 

 his. Winge also figured the feet and the heads in profile view, 

 showing the ears and vibrisste of some genera of Loncherin^. 

 Boas also (' Ohrknorpel der Saugthiere,' p. 119 et seq., 1912) 

 described the ears of some genera, figuring those of Cavia, 

 Basyprocta, Gcelorjenys, Hydrochcerus, Lmjostomus, and Hystrix. 



The observations set forth in the following pages have been 

 taken mainly from fresh material examined immediately after 

 death in the Society's Prosectorium. This has been supplemented 

 by specimens preserved in alcohol in the Society's collection, and 

 by dried skins where soft material was unavaihxble. 



The Rhinarium. 



In Hystrix and Atherura the rhinarium is ill-defined. In 

 Hystrix it is hairy to the edge of the nostrils. In Atherura 

 there is an area of naked skin both above and below these 

 orifices. In both genera the nostrils are transversely elongated 

 slits, expanding anteriorly and internally; and there is a very 

 well-defined smooth philtrum, completely dividing the upper lijp 

 into its right and left moieties, which are independently movable 

 (Text-fig. 1, A-C.) 



The rhinarium of Thrynomys is well defined, although the 

 hair encroaches upon it above and beneath laterally, leaving only 

 a narrow naked rim above and below the nostrils, which are 

 tolerably widely separated. It extends, as in Hystrix, to the 

 edge of the upper lip, forming a philtrum, wider above than 

 below, and completely dividing the lip into a right and left 

 portion. (Text- fig. 1, D.) 



In Dinomys, according to Peters, the upper lip is deeply cleft — 

 apparently very much as in Hystrix and Atherura ; and above 

 it there is a distinct triangular rhinarium, naked in front and 

 round the nostrils, but hairy above owing to the forward extension 

 of the hair of the muzzle well in advance of the posterior ends 

 of the nostrils, which are described as S-shaped, a form these 

 orifices assume in many of the Hystricomorphs *. 



Dinomys is the only American genus of Hystricomorphs, so far 



* Peters seems to li;ive regarded Diwunys as akin to Coelogeni/s. He appears to 

 have been misled in this matter by the similarity in colour between the two o-enera 

 There is, however, no obvious evidence of kinship between them. 



25* 



