424 Mii. R. I. rococK on the external 



Judging from dried skins, the genus is distinguished by the 

 cleavage of the upper lip by the rhinariuin, the Aalvidar supra- 

 tragus — a character repeated in the Caviinpe,— and the structure 

 of the feet. The affinities of the family appear to me to be quite 

 doul)tful. 



Family DiNOMYiDiE. 



I can give no opinion about Dinomys beyond expressing my 

 conviction that it is not in any way nearly related, as Peters 

 thought, to the Dasyproctida?, Chinchillida^, or Caviidfe in the 

 sense in which he understood those terms. It must remain as 

 tlie sole representative of a well-mai'ked famih-. 



Families Dasyproctid^ and Ccelggenyid^, nov. 



So far as I a,m aware, no suggestion has been made to break 

 un the family Dasyj^roctidfe as understood by earlier authors. 

 The tendency rather has been to merge it witli the Caviidse, as 

 was done by Winge, Tullberg, and Weber, Three genera are 

 now admitted — Dasyiwocta, Myoprocta^ and Coilogenys. The first 

 two are closely related ; but it appears to me that the value of 

 the well-known distinctive features of Coelogenys have been 

 greatly underrated. I propose to erect it to the i-ank of a family, 

 which may be distinguished fi'om the Dasyproctidfe (s. s.) as 

 follows : — 



a. Autemolar portion of palate broad and nearlj- flat ; pvseorLital t'ova- 

 men, zj'gomatic arch, and orbit without special modifications; 

 nasals as long as tVontals or nearly so ; postorbital part of skull 

 comparatively long and narrow ; occipital crest irregnlailj^ semi- 

 elliptical. No cheek-pouches. Feet long and slender ; fore foot 

 nearly perissodactyle, with fifth digit tolerably widely separated 

 from fomtli ; plantar pad bilobate, the outer lobe, if represented, 

 indicated merely by a small circular scale at the base of the fifth 

 digit and remote from the rest of the pad. Hind foot with only 

 three toes and a small plantar pad Dastpeoctidj;. 



a'. Antemolar portion of palate strongly compressed, forming a median 

 ridge deeply grooved and bicarinato almost to the incisors; the 

 whole zygomatic arch profoundly modified mainly by the out- 

 growth from its maxillar3' and malar portion of a great bony 

 lamina forming a cheek-plate extending downwards to overlap and 

 conceal the greater part of the mandible; the maxillary portion of 

 the arch is deeply hollowed beneath and is continued forwards as 

 far as the premaxillary suture, the roof of the hollow forming the 

 floor of the preoi-bital foramen which is convert'^d into a long deep 

 channel in front of the orbit, and the orbit itself is reduced in 

 dimensions by the upgrowth of its inferior edge and looks obliquely' 

 outwards and upwards; nasals uiuch shorter than frontals, post- 

 orbital portion of skull wide and short, occipital crest nearly semi- 

 circular. Large cheek-pouches present. Feet short and robust, 

 fore foot nearly artiodactyle, with four main digits evenly spaced, 

 the plantar pad large with outer lobe well developed and confluent 

 with median ; hind foot with five digits Ccelogentidj];. 



So far as the feet ai'e concerned, Codogenys is a much more 

 primitive type than Dasyprocta, and might be regarded as 



