1884.] MURID.E FROM CENTRAL PERU. 453 



that the points of difference between tliem and H. laticeps are all 

 such as are explainable on ordinary climatic grounds, supposing that 

 their home is hotter than the places in which H. laticeps ordinarily 

 lives. 



They are characterized by tiieir dark rich rufous colour, apparently 

 pure white bellies, though the hairs are slate-coloured at their 

 bases, longer tails, bicolor for their proximal inch,' proportionately 

 longer hind feet, and larger ears. Their skulls are quite similar to 

 those of the true H. laticeps. 



In this variety we have, so to speak, the commencement of a species, 

 which appears to be gradually becoming differentiated from another 

 common and widely-spread form, and which will possibly in the 

 future become more and more distinct i'rom its parent, as the 

 individuals representing the intermediate stages die out, until it is 

 itself worthy to rank as a separate species. 



[Hesperomys (Oryzomys) galapagoensis, Waterh. 



Two skins of this species were obtained by M. Stolzmann at 

 Tumbez in North Peru, but were not sent to me in time to be 

 included in my account of his collection. As the occurrence of this 

 species on the mainland has not been hitherto publislied, I take this 

 opportunity of recording the fact of its presence in Peru. There are 

 also two specimens of it in the British Museum, collected by 

 Mr. Fraser in Ecuador.] 



4. Hesperomys (Oryzomys) longicaudatus, Benn. S. No. 6. 



a to c. Two specimens (a and h) from Amable Maria, 2000 feet, 

 and one (c) without special locality. 



Specimen c is of a much lighter colour than usual, and differs in 

 certain other unimportant respects from ordinary //. lonfjicaudatus, 

 but may be considered for the present to represent only a pale 

 variety of that species. 



5. Hesperomys (Oryzomys) spinosus, Thos. S. No. 7. 

 a. Amable Maria, b. No special locality. 



These specimens are in every res])ect like the types of this 

 interesting species, described from M. Stolzmann's collection. 



