386 Zoological Society : — 



rieties, in which we should expect to find the most constant, and 

 therefore most vahiable differences, should any exist, present no 

 variety amongst themselves, excepting that of size ; and in this latter 

 respect they bear an exact relation to the varieties to which they 

 belong. 



With a series of specimens before me illustrating this, I have ex- 

 tended the same geographical and anatomical tests to the so-called 

 varieties of the present genus. The results of this attempt were by 

 no means similar to those observed of the Indian species ; for instead 

 of meeting with anything like the gradation which occurs there, I 

 have found that the largest and the smallest examples were alike in- 

 habitants of Western Australia ; whilst a third, which in point of 

 size would have served to unite the two, was separated from them 

 by a wide interval, occurring on the coast of New South Wales. This 

 led to a re-examination of the specimens, and more especially to a 

 comparison of their crania. They were found to be very dissimilar. 



Here, then, are two instances, one in which the variation is clearly 

 traceable to an external cause, and accompanied by a uniformity of 

 internal structure, thereby corroborating the unity of the species ; 

 and another, in which the variation is not due to any apparent 

 cause, and not only unsupported by anatomical similarity, but the 

 unity of the species is absolutely disproved by the existence of very 

 diverse osteological characters. 



Without dwelling longer on this subject, I may observe, that 

 these remarks have arisen, in the first place, from the consideration 

 of some exceedingly judicious observations on the variation of species, 

 delivered at the Meeting of the British Association at Cheltenham in 

 1856, by the Rev. Leonard Jenyns. I must refer the reader to the 

 communication printed entire in the Report of the Proceedings of the 

 Association for that year, and content myself with observing that 

 that gentleman urged the necessity of duly considering the influ- 

 ence of climatal and other causes in producing varieties of species ; 

 and also pointed out, that, in the absence of any such causes, any 

 considerable amount of difference from a known species might be 

 regarded as strong distinctive evidence. 



Since the preceding account was written, I have obtained another 

 specimen of Nyctophilus Timoriensis, collected in some part of Au- 

 stralia, but I do not know the exact locality. 



As it is preserved in spirit, and in good condition, I am enabled 

 to give a better account of the form of the face and nose-leaves than 

 that already given, and thus add at the same time to the specific and 

 generic characters. 



The first nose-leaf is slightly emarginate and rises from imme- 

 diately above the nostrils, in such a manner as to give the end of the 

 nose somewhat the appearance of a disc, in which the nostrils are 

 pierced. Between them and the nose-leaf, however, is a deepish 

 transverse depression, with two pits, one over each nostril, which in 

 some measure destroys the regular disc-like appearance of the end 

 of the snout. The nostrils themselves are pear-shaped, with the 



