EXTERNAL CHARACTERS OF SOME HYSTRICOMORPH RODENTS. 365 



21. On Llie External Cliaractei's of some Hystricomorph 

 Rodents. By R. I. PococK, F.R.S., F.Z.S. 



[Received February 7, 1922 : Read March 21, 1922.] 



(Text-figures 1-28.) 



Contents. Pa^e 



Introduction 365 



Rhinnrium 337 



Facial Vibrissa; 37I 



Moutli and Cheek-pouches 374 



■Ear 376 



Feet 383 



Genital Organs of Male 403 



Genital Organs of Female 4I3 



Anus 415 



Tail 420 



Notes on Families and Subfamilies 422 



Introdi(,ction. 



The classifications of the Hystricomorpha in English text-books 

 of Zoology are based upon the one proposed by Alston in 1876 

 (P. Z. >S. 1876, pp. 90-97), which was itself an amplification and 

 in some particulars a modification of the arrangement suggested 

 by Waterhouse in 1848. Alston added to the group the'family 

 Dinomyidae, which, following Peters, he placed between the 

 Dasyproctidfe and Caviidse ; and the Ctenodactylin^, which he 

 ranked as a subfamily of Octodontidje. He also transferred 

 Petromys from the Echymyina (Echinomyinje), where it was 

 placed by Waterhouse, to the Octodontinae. 



His system, adopted to the letter by Flower and Lydekker 

 (' Mammals Living and Extinct,' pp. 484-491), was as follows: — 



Hystricomorpha. 



1. Octodontidas. 



Ctenodactylinae (^Ctenodactylus, Pectinator). 



Octodontina? {Petromys, Ctenomys, Schizodon, Spcdaco2ms, 



Octodon, Abroconia). 

 Echinomyinpe (Carterodon, Myopotcmms, Cer corny s, Lon- 



cheres, Mesomys, Ecliinomys, Dactylomys, Plagiodontia, 



Capj^omys, Atdacodus). 



2. Hystricidse. 



Sphingurin£e {Ch(Etomys, Sjylnngurus, Enjthizon). 

 Hystricinae [Atherura, Hystrix). 



3. Chinchillidse {ChinchUla, Lagidmm, Lagostoinus). 



4. Dasyproctidae {Dasyj^rocta, Cadogenys). 



5. Dinomyidae (Dinomys). 



6. Caviidae (Cavia, DoUchotis, Hydrocluerus) 



Proc. Zool. See— 1922, No. XXV. 25 



