CHARACTERS OF SOME HYSTIiICOMOH^lI RODENTS. 371 



In Hydrochcenis the rhinarium is scarcely defined, although 

 the skin between the nostrils is naked. The nostrils are very 

 widely separated and small, without any postero-lateral slit 

 The upper lip is exceedingly deep and naked or scantily haiiy 

 in the middle. 



The rhinarium of Gtenodactylus is continued to the edge of the 

 upper lip by a naked area of skin, which, like the rhinarium 

 itself, is capable of lateral compression, being broad or narrow 

 according to the degree of contraction of the muzzle. The upper 

 end of this labial tract is continued on each side as a naked rim 

 beneath the nostrils. The upper edge of the rhinaiium is 

 convex with a median angular emargination. The area above 

 the nostrils is deep ; the nostrils themselves when expanded are 

 large orifices with very short posterior slits, and the narrow space 

 between them is marked by a deep median groove extending 

 from the top of the labial ti-act to the summit of the rhinarium. 

 (Text-fig. 4, G.) 



In view of the former association of Gtenodactylus with the 

 Jerboas (Jaculidse) it is interesting to note the close similarity 

 between that genus and Jaculii,s in the rhinarium, not only in 

 structural details but in its compressibility. 



Facial Vibrissce. 



In P. Z. S. 1914, pp. 903-905, I described briefly the facial 

 vibrisstB of several species of Hystricomorpha belonging to the 

 genera Atherura, Coendu, Erethizon, Octodon, Chinchilla, Lago- 

 stomas, Dolichotis, Coilogenys, Dasyprocta, Gavia, and Hydro- 

 choerus, and showed the general constancy of the presence of 

 well-developed mystacial, superciliary, and genal tufts, the latter 

 being usually set high up the face near or even behind the 

 posterior angle of the eye. Since then I have extended my 

 observations, and can add several more species to the list. 



In Hystrix, Acanthion, Atherura, and Trichys the vibrissse are 

 as originally desci^bed in Atherura, namely, exceedingly long 

 and well developed, and there is always an interramal tuft. In 

 Thrynomys, on the contrary, although its mode of life is tolerably 

 similar to that of the Old World Porcupines, the mystacials are 

 comparatively slender and short, and in two dried skins I can 

 find no trace either of superciliary, genal, or interramal tufts in 

 the coarse hairs clothing the head. Peters described the mysta- 

 cials as long in Dinomys and the genals as set behind the eye, 

 but says nothing about the interramal tuft. 



In the genera of Loncherinse figured by Winge, namely, 

 Loncheres, Echimys, Cannahateomys, Trichomys {Nelomys), 

 Garterodon, and Mesomys, well-developed mystacial, superciliary, 

 and genal vibrissfe, the latter behind the eye, are shown, but no 

 interramal tuft is indicated. The omission of the interramal tuft 

 can hardly be taken as proof of its absence in these genera. 

 Nevertheless, I failed to find it in examples of Gtenoritys and 



