448 MR. O. THOMAS ON A COLLECTION OF [JlUlO 1/, 



from a different locality enabling us to increase somewhat our scanty 

 knowledge of the Peruvian Muridae. 



The collection consists of no less than 92 specimens, belonging to 

 12 species, of which one belongs to Holochilus, one to Rheithrodon, 

 and the remainder to Hesperomys, representing the subgenera 

 Rhipidomys (1), Oryzomys (3), Calomys (1), Vesperimus (1), and 

 Habrothrix (4). Of these, one species, Rheithrodon pictus, is new; and 

 two, Hesperomys laticeps, var. nitidus, and//. bimaculatus,vnv.lepidus, 

 represent new varieties of species already described. Good series of 

 specimens of each of the new forms are in the collection, so that 

 their characters and variability, so far as occurs at a single locality, 

 can be fairly made out. 



In the suhgeneric names used in 1882 I simply accepted the 

 groups as defined by Baird 1 , and used by other authors up to the 

 present time ; but on a closer investigation I find that the subgenera 

 proposed by Waterhouse 2 in 1837 should stand to a much greater 

 extent than was allowed by Baird, who merely went upon Water- 

 house's descriptions, without seeing any specimens of such subgenera 

 as Phyllotis, Calomys, or Scapteromys, each of which is fully entitled 

 to the same rank as the other groups. 



The following are the subgenera into which the unwieldy genus 

 Hesperomys may be most satisfactorily divided : — 



Rhipidomys, Tschudi. — Form myoxine ; tail long, hairy, pen- 

 cilled at the tip ; feet very short, broad, with large sole- 

 pads ; mammae 1 or 0-2 = 6 or 4 ; interdental palate-ridges 

 5 or 6. 



Skull with the cranial portion very large as compared to 

 the facial ; interparietal large ; supraorbital margins ridged ; 

 palatal foramen of medium length. 



Teeth large, their pattern as in the larger Oryzomys. 

 Species : — H. leucodactylus, Tsch. (type), H. latimanus, Tomes, 

 H. pyrrhorhinus, Wied., H. sumichrasti, De Sauss., and 

 (?) H. bicolor, Tomes. 

 Range. Amazonian Subregion, Ecuador, and Peru. 



Oryzomys, Baird. — Form murine ; tail long, scaly ; feet long ; 

 soles quite naked; mammae 2-2 = 8; interdental palate- 

 ridges 5. 



Skull generally strongly made ; supraorbital edges and 

 palatine foramina various. 



Teeth with broad, low, complex crowns, the folds in which 

 remain until old age. 

 Species: — H. palustris, Hail, (type), H. anyouya, Desm., H. 

 albigularis, Tomes, //. galapagoensis, Waterh., H. longi- 

 caudatus, Benn., H. spinosus, Thos., &c, &c, nearlv 30 in 

 all. 

 Range. Southern United States to Cape Horn, most numerous 

 in the more tropical districts. 



1 Mamm. N. Am. p. 454 (1859). 2 P.Z. S. 1837, p. 20. 



