4i2 Mr. O. Thomas on 



LXVIII. — Xotes on Suuth- American Rodents. 

 By Olufield Tuomas. 



I. — A new Name for Sciuvus Roberti, Thos. 



In 1903 * I gave to an Eastern Brazilian squirrel tlie above 

 name in honour of its discoverer Mr. Alphoiise Robert. But 

 two years before f Mr. Botihote had already u.sed tlie same 

 term lor a squirrel obtained by Mr. Robert Ssvinhoe in 

 Formosa, and I would therefore propose for the Brazilian 

 species the name of Sciurus Alphonsei. 



II. — On the Allocation of certain Species hitherto referred 

 respectively to Oryzomys, Thomasomys, and Rhipidomys. 



In connexion with Mr. W. H. Osgood's work on the genus 

 Peromyscus^ my attention has been drawn by him to the 

 characters that distingui.^h the group containing " Hesperomys 

 {Uliipidomys') cinereus, Thos./' which was made the tj'pe of 

 a special genus '■^Thomasomys" by Dr. Elliott Coues in 1884 \. 

 But with the exception of one more recent description of 

 my own, the name has hitherto been practically ignored. It 

 is used, however, in Trouessart's Catalogue on the authority 

 of that one description. 



Now, however, a revision of a number of the species 

 concerned shows that Thomasomys (the cacophony of whose 

 name I deplore) is a well-defined group, containing a con- 

 siderable number of species, and that it may be distinguished 

 from Oryzomys by certain characters of the palate, well shown 

 in some admirable figures published by Mr. Outrani Bangs 

 in 1900 §, and by the ]iossession, in most of the species, of 

 only 1 — 2 = 6 niarama^, as compared with the invariable 

 2 — 2 = 8 of Oryzomys. 



In Oryzomys (including the subgenus Oligoryzomys, Bangs) 

 the palate extends some distance behind tiie posterior border 

 of the last molar, the palatal notch is narrowed or pointed, 

 and on each side of it, between m^ and the corner of the 

 mesoptcrygoid fossa ||, there is a small pit or pair of pits, 



* Ann. & Mag. Nat. Hist. (7) xii. p. 463 (1903). 



t Sciurus thaiuanensis lioberti, Ann. & Mag. Nat. Hist. (7) vii. p. 160 

 (1901). 



X Am. Nat. xviii. p. 1275 (1884). 



§ Proc. New England Zool. Club, i. p. 94, pi. i. (UXK)). 



II A good deal of confusion ha^ arisen as to the use of the words nieso- 

 and interjiterygoid for tbe foss;v situated («) between the pterygoids iu 

 the middle line and (h) those phiced laterally between the eeto- and 

 entopterygoids of either t.ide. the former being median and mipairod. the 



