192 Mr. 0. Thomas on the So u(h- American 



XIX. — On the Arrangement of the South American Rats allied 

 to Oryzomys and Kliipidomys. By Oldfield Thomas. 



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



Whex writing some years ago* on the relation of Oryzomys 

 and Rhip'tdomys to each other and the allied forms Thomas- 

 oniys and CEcumys, with lists of the forms belonging to each, 

 1 indicated certain species as of doubtful position, and I 

 have now had an opportunity to re-examine these in the light 

 of furtlier material. 



As then explained, all these rats are divisible into two 

 groups, those with the structure of tiie palate as in Oryzomys 

 {Oryzomys and (Ecomys) and those with it as described and 

 figured by Bangs f in his '^ Erioryzomys" [RHipidomys and 

 T/iomasomys). Of the first of these groups only one species, 

 ^^ Hesperomys ^' riifesceiis, was referred to as doubtful, and 

 of tliis animal an additional example, without locality, has 

 lately been found among some old specimens put aside as 

 duplicates, and I have therefore been able to make a further 

 study of it. 



The second specimen, although its skull is very dilapidated, 

 happens to show the posterior palate, and is also much 

 younger than the type, with almost unworn teeth, so that 

 an opinion can be formed as to its systematic position. 



On studying the characters observable on the two 

 specimens I find that the animal, while belonging to the 

 Oryzomys-CEcomys series, certainly represents a genus dis- 

 tinct from any of its allies, its molar structure being indeed 

 quite unique in the group. 



It may be called ; — 



Rhagomys, gen. nov. 



General facies about as in (Ecomys. Feet modified for 

 an arboreal life, with large plantar and digital pads. Mammse 

 apjiarently 1 — 2 = 6, as in Rhipidomys. 



Skull broad and low, with broad, smooth, rounded brain- 

 case; supraorbital edges square, not ridged. Zygomatic 



• Ann. Majr. X. H. (7) xviii. p. 442 (1906). 



t P. Xew Engl. Zool. Club, i. p. 96, pi. i. fig. 3 (1900). 



