250 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXV. 



aged, or an aged individ^la1. But when it comes to the question 

 of months or years, we must give it up. 



I consider this question, as to the actual age of a given individual, 

 for practical purposes more important than the question of its 

 possible extreme span of life (but the solution of the forcter will, of 

 course, ultimatel_y lead to the solution of the latter, as we shall spe 

 later on). To give one instance among many. Certain Horseshoe- 

 bats show a truly bewildering " variability" in the colour of their 

 fur, and the Indian Rhinolophns rouxi is in this respect one of the 

 most perplexing of all. Have these coloui- "variations" anything 

 to do with the sex or season (these questions it ought to be possible 

 to settle at once by reference to the labels of the specimens) or 

 with the age of the individuals ? ] have had to attack this problem 

 lately, when working out for the British Museum " Catalogue of 

 Chiroptera" the unusually fine series of Eli. rouxi collected by Mr. 

 Gu)^ C. Shoi'tridge for the Bombay Natural History Society's 

 Mammal Survey of India,'* and it has naturally induced me to 

 study more closely the different stages of wear of the teeth, with 

 the object of finding in them a possible means to determine the 

 age of each individvial. This paper gives my conclusions. 



A few words to explain my method. To eliminate, as far as 

 possible, all sources of error, should be our first consideration. An 

 ideal material would therefore be this : — We require, as a basis, to 

 begin with, a series of specimens all collected approximately on one 

 day or at least within the space of about a month, and showing all 

 stages of wear of the teeth ; provided they really show all degrees 

 of Avear found on that date or in that month, we shall be able to 

 sort them out in so and so many stages, separated by one year. In 

 many cases we should require an enormous series of individuals in 

 order to have all stages represented, in others, with more good luck, 

 a much smaller series will contain all the stages. Further, this 

 series ought to be collected, if not exactly on the same spot, at - 

 least within the same faunistic area, to make reasonably sure that 

 differences in food have not influenced the degree of wear of the 

 teeth. If we have succeeded so far, we still require oxry amount of 

 material of the same species from every " other month of the yeai- 

 (but preferably from the same area), in order to check the results 

 we obtained by our first series. 



It would be too much to say that the Shortridge material fulfils, 

 absolutely, these ideal conditions, but it comes sufficiently close to 

 them to be workable. It contains forty individuals, not from one 

 month, but from two consecutive months, viz., October aiad Novem- 

 ber, all from the same district, and 1 have reason to believe thai 



* See my paper " On the so-called colour i)hiises of the Rufous Horscshoe- 

 batof India" {Rhinolophns rouxi, Temm.), this Journal, infra. 



