536 
COMPENDIUM OF GEOGRAPHY AND TRAVEL 
as to forbid the existence of many mammals, we find a 
curiously rich and highly specialised avifauna, and a still 
more astonishing development of the land mollusca. The 
richness of the Passerine birds is most strongly marked 
in the Drepanididce -, of which there are no less than 32 
representatives, most of them belonging to the genera 
Himatione and Hemignathus . The latter genus is 
characterised by the extraordinary peculiarity of the 
prolongation of the upper mandible, so that in some cases 
it is twice the length of the lower, or even more, and the 
genus may be regarded as a midway form between the 
original immigrants and the more highly specialised 
Drepanis , with long, curved, and equal mandibles. Until 
recently these birds were regarded as Meliphagine, and 
therefore as having their nearest affinities in the Australian 
region, but Dr. Hans Gadow has recently proved con- 
