140 Mr. O. Thomas on 



XIII. — On Spinji Rats of the Proecliimys Group from 

 South-eastern Brazil. By Oldfield ThOMAS. 



(Published by permission of the 'rrustee.s of the British Museum.) 



The spitiy rats referable to Proechimys that occur in South- 

 eastern Brazil, Bahia, Rio Janeiro, &,'^., have for long- been 

 in an excessive state of contusion, mainly owing to the fact 

 that the species to which the earlier names — setosu.i^ myosurus, 

 albispinus, and others — were applicable had never been 

 properly identified. 



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

 Briti.sh Museum, and, in addition, have had the advantage, 

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

 skulls o£ Echimys setosus, Desm.,and E. albispmus^ I. Geotf., 

 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 tlie original E, albispinus of Bahia. 



The species that occur in the area referred to prove to be 

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

 distinct groups, which may be considered as of subgeneric 

 importance — namely, Proechimys^ s. s., and Trinomys, suhg. n. 



The primary distinction between these lies in the number 

 of lamin?e present in the cheek-teeth — four in Proechimys, 

 three in Trinomys, — while, in addition, the skull oi' Trinotnys 

 is less elongiite, with shorter 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 another 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,v^\\\Q\\, 

 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 p'*' is always quadri- 

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

 considered the genotype of Trinomys. 



The five species of 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 oini^. (Minas Geraes.) .. 1. roberti, Thos. 



