158 report— 1878. 



cases must be left for consideration when they arise, and that a higher co- 

 efficient may be then allowed in those instances where the reasons given 

 appear to the Board of Trade to justify it. 



" We are, &c, 



(Signed) "John Hawkshaw, 



"W. YOLLAND, 



" W. H. Barlow. 

 " The Secretary of the Board of Trade, &c." 



This Report has since been acted upon by the Board of Trade in the 

 printed paper issued by them in reference to railway structures. 



It will be observed that a co-efficient of 6^ tons per square inch is 

 assigned to steel, that of iron being 5 tons per square inch. 



This increase of the co-efficient will effect important economy in 

 structures, especially in bridges of large spans, and will also tend gene- 

 rally to increase the employment of steel for railway and shipbuilding 

 purposes. 



The labours of your Committee having ended in such a satisfactory 

 manner, there is no necessity to reappoint them. 



Report on the Geographical Distribution of the Chiroptera. 

 By Gr. E. Dobson, M.A., M.B. 



[A communication ordered by the General Committee to be printed in externa 



among the Reports.] 



In his work on the Geographical Disti'ibution of Animals, published 

 scarcely two years ago, Mr. Wallace writes : — " The genera of Chiroptera 

 are in a state of great confusion, the names used by different authors 

 being often not at all comparable, so that the few details given of the 

 distribution of the bats are not trustworthy. We have therefore made 

 little use of this order in the theoretical part of the work." And again : 

 " The bats are a very difficult study, and it is quite uncertain how many 

 distinct species there are ; the genera are exceedingly numerous, but they 

 are in a very unsettled state, and the synonymy is exceedingly confused. 

 The details of their distribution cannot therefore be usefully entered upon 

 here." 



These remarks furnish a suitable preface to this paper. The recent 

 publication of my work on the Chiroptera renders them, I hope, no longer 

 applicable, and I purpose now to set forth in greater detail the results of 

 my inquiries into the geographical distribution of these animals than the 

 space at my disposal in the introduction to the work referred to has per- 

 mitted. 



Mr. Wallace points out the pre-eminent importance of the distribution 

 of Mammals in determining the limits of zoological regions ; but also 

 remarks that, " there are two groups which have quite exceptional means 

 of dispersal — the bats which fly, and the cetacea, seals, &c., which swim. 

 The former are capable of traversing considerable spaces of sea, since two 



