Jklr. O. Thomas on some Mexican Oryzorays. 403 



Hesperomys Couesi, Alston. 

 Hesperomys Couesi, Alston, P. Z. S. 1876, p. 756. 



This species, described by Alston from three specimens now 

 in the British Museum, has proved rather a stumbling-block 

 to later workers, and this is not surprising, as an examination 

 of his specimen shows that the three examples represent 

 certainly two, and perhaps three, different species. The 

 question therefore that at once arises is as to which of the 

 three should be taken as tlie type, a question which, on the 

 principle of the selection of the iirst-named species as the 

 type of a genus, may best be settled by taking Mr. Alston's 

 specimen a as the type of //. Couesi. This selection is 

 supported both by the fact that the first five lines of the 

 description itself are solely based on the spirit-specimen and 

 also by Mr. Alston's known partiality to working on alcoholic 

 material ; so that no one who knew his methods would doubt 

 as to which he himself would have chosen. I propose there- 

 fore for the future to look upon Mr. Salvin's spirit-specimen 

 from Coban, Guatemala, whose measurements are given in 

 Mr. Alston's first column, as the tjpe of his //. Couesi. 



Whether c, from Mexico [Verreaux) , is or is not the same 

 species I am at present unable definitely to decide ; but that b 

 is distinct from either is perfectly clear, its distinctive cha- 

 racters, both cranial and external, being more definite than 

 are those separating any other two members of this difficult 

 group. 



The true 0. Couesi, as represented by the type specimen, is 

 a small species with slender limbs and long tail. Its colour 

 is fulvous, darker along the centre of the back and paler, but 

 not white, on the belly. The ftir is fairly soft, but not thick 

 and woolly as Alston stated, that remark evidently resting on 

 specimen h (my 0. fulgens). The measurements of the 

 typical skull are given below and also those of the skull of an 

 old male from the Hacienda Cubilguitz, about 25 miles north 

 of Coban, which with some hesitation I refer to this species. 



Oryzomys fulgens, sp. n. 



Size large. Fur very thick, coarse, and woolly. General 

 colour above bright fulvous, brighter than in any other 

 Central- American species ; anterior half of the body, including 

 the head, rather paler and duller than the posterior half. 

 Ears decidedly small, broadly rounded, thinly hairy, their 

 hairs practically the same colour as those of the head in 

 general, so that they are not distinguishable by colour at a 



