of two British Species of PlecotuS. 57 



manus. On the other hand, in the P. auritus the thumb is 

 somewhat shorter, and the tail not so much exserted from 

 the interfemoral membrane ; of which last part it may be also 

 added, that in the P. hremmamis its extreme tip terminates in a 

 fine point, whilst in the P. auritus it is somewhat obtuse and 

 flattened. Another, and perhaps the most obvious distinction, 

 resides in the expansion of the flying membrane, which, viewed 

 relatively as well as absolutely, is by much the more considerable 

 in the P. auritus. This circumstance arises from the greater 

 development of the metacarpal bones and the phalanges of the 

 fingers, as compared with the arm and forearm. In the P. au- 

 ritus, the length of the middle finger, or the distance measured 

 from the carpus to the apex of the wing, exceeds in length the 

 arm and forearm together by three lines, and the forearm taken 

 separately by more than an inch ; whereas in the P. brevi- 

 manus the length of this part is less than that of the arm and 

 forearm together, and only exceeds the forearm separately by 

 six lines. It is with a view to this last peculiarity that I have 

 selected the trivial name of this species. Lastly, I may remark, 

 that in the P. brevimamis there is a shallow notch on each side 

 of the interfemoral membrane, about halfway between the heel 

 and the extremity of the tail, which in the P. auritus is scarcely 

 visible. 



The above distinctions, many of which are founded upon a 

 comparative view of the osteology of the two species, can 

 scarcely be considered as the variations of a different age. In- 

 dependently of them, however, these bats, when seen together, 

 will not be easily confounded, from the great difference in their 

 absolute size, and in the colour, — more especially of their under 

 parts. In the P. auritus, the colour is brownish-grey mixed 

 with dusky, and is nearly the same above and below, being in 

 the last instance merely of a somewhat paler tint. In the P. bre~ 



VOL. XVI. I vimanus. 



