140 Mr. O. Thomas on 



XIII. — On ^piny Rats of the, Proecliimys Group from 

 South-eastern Brazil. By Oldfield TuOMA.S. 



(Published by permission of tlie Trustees of the British Museum.) 



The spiny rats referable to PvoecJiimys that occur in South- 

 eastern Brazil, Bahia, Rio Jaueiio, tfec, have for lon^- been 

 in an excessive state o£ contusion, mainly owing to the fact 

 that the species to which the earlier names — setosia^, mz/osurus-, 

 albispinus, and others — were applicable had never been 

 properly identified. 



Now, however, I iiave been through the material in the 

 British Museum, and, in addition, have had the advantage, 

 by the kindness of Dr. R. Anthony, of examining the typical 

 skulls of Echimys setosus, Desm.,and E. albispmus, I. Geoif., 

 while Dr. Winge has given me information about Loncheres 

 elegans, Lund. Furthermore, Dr. Bedot and M. Revilliod, of 

 Geneva, have been so good as to lend me two additional 

 examples representing the original E. albispinus of Bahia. 



The species that occur in the area referi'ed to prove to be 

 no less than five in number, and they belong to two very 

 distinct groups, which niay be considered as of subgeneric 

 importance — namely, Froechimys, s. s., and Trinomys, suhg. n. 

 The primary distinction between these lies in the number 

 of laminae present in the cheek-teeth — four in Proechimys, 

 three in Trinoinys, — wliile, in addition, the skull of Trinotnys 

 is less elongate, with shoiter muzzle, less-developed supra- 

 orbital and parietal ridges, and orthodont or slightly proodont 

 incisors, as compared with the opisthodont incisors of Pro- 

 echimys. In all characters, however, the species grade too 

 muchinto one anotiier to consider the groups as genera, espe- 

 cially as the most important point, the number of the tooth 

 laminae, has a curious exception — Proechimys vacillator ,\y\\[c\) , 

 as explained in the original description, has a variable number 

 of its cheek-teeth trilaminate, while it is in all other respects 

 typically Proechimys^ with long skull^ strong ridges, and 

 opisthodont incisors ; and in any case jo* is always quadri- 

 laminate. P. albispinus, as being the most extreme, may be 

 considered the genotype of Trinomys. 



The five species ot the area, with the addition of a new 

 subspecies to P. albispinus, may be sorted as follows: — 



A. With 4 laminae to cheek-teeth. — Pro- 

 echimys, s. s. 

 a. Skull with strong ridges and post- 

 orbital angles. Palatal notch to 

 middle oi »i^. (Minas Geraes.) . . 1. rohertl, Thos, 



