CHARACTERS OF SOME IiySTRICOMORPH RODENTS. 379 



to the auditory orifice as in Capromys and Hystrix, curves some- 

 what backwards beneath the supratragus and loses itself in a 

 thickening occupying the cavity of the ear above the orifice, 

 (Text-fig. 6, A, B.) 



In the ear of Octodon the laminate portion is widely expanded, 

 especially below behind the antitragal area, but the edge above 

 this is distinctly emarginate. The cavity is, however, capacious, 

 although the supratragus which borders it above and in front does 

 not stand out as a definite shelf-like ridge. Tiie extension of 

 the antero-internal ridge curves backwards and then upwards, 

 detining a deep pit as in Ooelogenys and Lagostoinus. The tragus 

 is reduced to a little excrescence, not concealing the orifice which 

 lies behind the ridge forming the anterior border of the unusually 

 elongated notch (aditus inferior). The antitragus is very large 

 and fieshy, but has no trace of poach. (Text-fig. 6, I.) 



r.n the six genera of Loncherine Octodontidse figured by 

 Winge, namely, Loncheres, Echimys, Gannahateomys^ Trichomys 

 {Nelomys), Garterodon, and Mesomys, the ears are apparently 

 simple in type, moderately large or small in size, and stand away 

 from the head inferiorly from a point beneatli the antitragus or 

 the notch in front of it, which is distinct in all of them. The 

 anterior edge is folded over from a point below the anterior end 

 of tlie supratragus, its inferior end carving backwards and down- 

 wards into the cavity of the ear, this curvature being especially 

 strongly marked and high up in Loncheres, where the ridge is 

 curled so as to circumscribe a definite pit as in Octodon. This 

 peculiarity is not so well marked in the other genera. In 

 Loncheres, too, the pinna is relatively smaller and the antitragus 

 larger. Garterodon has relatively the smallest antiti-agus of all. 

 The tragus is small in Echimys, Trichomys, and Gannahateomys, 

 and apparently undeveloped in the others. The supratragus 

 forms a simple, scarcely a shelf-like, ridge roofing the cavity of 

 the ear above anteriorly. The ]:)osterior border of the ear is 

 slio'htly emarginate a,nd angled above in Loncheres, Gannahate- 

 omys, Trichomys, and Mesomys, convex and angled in Garterodon, 

 nearly straight and quite unangled in Echimys. The inferior 

 portion behind the antitragus is well developed in all, but shows 

 no trace of a pouch. (Text-fig. 6, K, L.) 



Judging from the figures from which this description is taken, 

 the ears of all these genera are of a simpler, more primitive type 

 than those of Octodon degus. 



Judging from the illustration of Petromys, published by 

 A. Smith (lUustr. Zool. S. Africa, Mammalia, 1849) the ear 

 resembles that of the typical Octodontidse in a general way, but 

 details are not described or figured. 



The ear of Glenomys is greatly reduced and simplified in 

 adaptation to subterranean life. The apex is pointed ; the pos- 

 terior border is lightly concave above, but only stands freely away 

 from the head from a point a little below the supratragus, which 

 is not defined as a definite ridge, but is merely represented by the 



