54d Mr. o. THOMAS ON THE [May 3, 



of its spiny fur ; it is, however, a true Mus, and has no connexion 

 with the species of Leggada, the presence of spines being in no way 

 an essential character of that subgenus. 



"With regard to these spines, our series of M. coxinga from For- 

 mosa shows every stage, from a specimen almost entirely spineless to 

 one so thickly covered with spines that there are hardly any hairs. 

 Mr. Swinhoe, in his original description, stated that the number of 

 spines depended on age, the older specimens having the greater 

 number; but I think season has quite as much to do with it, as we 

 find specimens with the spines irregularly distributed in patches, as 

 if these specimens were changing their fur with the season. This 

 patchy arrangement, as far as one can see, could never obtain if 

 the spines increased regularly in number according to the age of the 

 individual. It seems probable, however, that both age and season 

 have some connexion with the number of spines developed. 



By the examination of such a series as that of M. coxinga and 

 others, we are irresistibly led to the conclusion that the presence of 

 spines in the fur, far from being a character of generic, or subgeneric, 

 is not even of specific importance. Dr. Jentink, of the Leyden 

 Museum, has recently', when describing various new species of Mus, 

 divided the species primarily into those with spines and those with- 

 out, laying great stress on this character. But I differ entirely from 

 him as to its value ; for not only have I seen, of the following Indian 

 species, specimens both with and without spines — M. alexandrinus 

 var. nitidus, M.fuhescens, 21. niveiventer, M. nitididus, and Ji. {Leg- 

 gada) hudnga, — but I have also observed the same thing in two 

 Fijian specimens of J/, exidans, Peale, and in the Central-American 

 genus Heteromijs, which normally has the fur altogether spinous. 



On the whole, therefore, I am inclined to think that in all tropical 

 countries, where the seasons of the year are tolerably well marked, a 

 development of spines takes place in the summer, these faUing off 

 again in the winter. Spines are presumably a much cooler covering 

 than hair, as all of the numerous spiny Rodents known are in- 

 habitants of tropical or subtropical countries, and none of places 

 with a distinctly cold climate. 



It is worthy of notice that it seems to be the species with the 

 finest and softest liair which have the greatest tendency to the de- 

 velopment of spines. Thus the coarse-haired Rats, such as Nesokia 

 bengalensis, M. decumanus, and M. alexandrinus var. riifescens, 

 seldom appear to produce true spines ; while, on the otherhand, the 

 fine-haired var. nitidus, J/, fulvescens, and J/, coxinga are at times 

 the most spiny of all. 



<^9. Mus NIVEIVENTER. 



*.¥. (Rattus) niviventer, Hodgs. J. A. S. B. v. p. 234 (1836). 



M. niviventer, Hodgs. Ann. & Mag. Nat. Hist. xv. p. 267 (1845) ; 

 Gray, Cat. Hodgson's Coll. (1) p. 18 (1846). 



Hab. The region bordering the Himalayas, from Simla to Kat- 

 mandu ; Darjiling {Jerdon) 1 



' Notes from the Leycleu Museum, i. p. 7 (1878). 



