CHARACTERS OF SOME HYSTRICOMORPH RODENTS. 369 



Dolichotis*, for example, in which there is a parting in the hairs 

 in the middle line of the upper lip which, especially in dried 

 skins, sometimes simulates a small philtrum ; but, although this 

 may be the remains of a true philtrum, it is very different from 

 that structure in HysUnx and Thrynomys. 



The rhinaria of Goendit and Erethizon differ greatly from 

 that of Hystrix. In Goenclu it is haiiy and the nostrils are 

 quite small and vertical rather than ti-ansverse in direction, the 

 postero-lateral slit being absent. In Erethizon the rhinarium is 

 marked by shorter hairs than that of the area round it. The 

 nostrils are larger and more transverse than in Coenchc and are 

 very close together, the space between them and their very 

 narrow upper edge being smooth. In neither genus is there a 

 philtrum. (Text-fig. 2, D, E.) 



In Capromys the rhinarium is large and naked, but not very 

 well defined laterally, where it passes into the short-haired area, 

 surrounding it above as well as laterally and below. It is marked 

 by a median groove in front. The nostrils are elongated and 

 expanded anteriorly. (Text-fig. 2, A, B.) In Myocastor the 

 I'hinarium is wider as compared with its depth than in 

 Capromys, the areas above and below the nostrils being much 

 narrower ; there is no median groove, and the nostrils them- 

 selves are much smaller, forming crescentrically valvular slits. 

 (Text-fig. 3, A.) 



In Gtenomys, Octodon, and Cavia the rhinarium forms a naked 

 area round the nostrils, the areas above and below these orifices 

 being narrow. (Text-fig. 4, C.) In Octodon it is mesially grooved 

 and angled below. In Ctenomys it has the upper edge biconvex 

 and mesially angled, the inferior edge transverse in the middle. 

 (Text-fig. 4, A, B.) In Cavia the nostrils are wider than in the 

 two Octodonts above described, the upper edge of the rhinarium 

 is concave, the lower convex from side to side, and there is 

 sometimes hair between the nostrils. (Text-fig. 4, F.) 



In Dolichotis patagonica the entire nose is large, with a wide 

 rhinarium concave in the middle and convex at the side above 

 and below, the finely hairy and tolerably deep areas bordering 

 the large transversely extended nostrils above and below being 

 thickened and muscular. In one example of this species the 

 internarial area was hairy in the middle line, whereas in an 

 example of D. salinicola it was naked ; but this character is 

 possibly not constant. (Text-fig. 3, D.) 



In Godogenys the upper rim of the nostril is swollen and 

 muscular, but the rhinarium itself is scarcely defined, being 

 covered with very fine short hairs, leaving only a narrow hairless 

 area above and below the elongated narrow nostrils. Judging 

 from dried skins the rhinarium of Dasyprocta is very similar. 

 (Text-fig. 3, B.) 



* I am not sure about tlie structure of tlie upper lip in Dasyprocta. The only 

 spirit example available had the rhinarium destroyed ; hut dried skins suggest the 

 absence of a complete philtrum. In living examples there appears to be a median 

 groove formed by a vertical fold in the skin of the upper lip. 



