382 Mr. R. Lydekker on 



nation of the affinities of their owners are matters of some 

 difficulty. There is moreover, doubtless, much to he done 

 in collecting bird-bones from these deposits, and also in re- 

 cording where specimens already collected are preserved; 

 and one of the results of the present article may be to direct 

 attention to these points. 



Since so few ornithologists have that intimate acquaintance 

 with those minute osteological differences in birds which are 

 essential for the determination of fossil specimens, it is some- 

 what difficult to write an article on the subject of fossil 

 birds, which shall not be, on the one hand, an elementary 

 treatise on avian osteology, or, on the other, Tjurdened with 

 technical expressions and terms, the meaning of which will 

 be found difficult to comprehend. Bearing in mind this 

 difficulty, it has been thought best to avoid osteological 

 descriptions as much as possible — merely pointing out, when 

 required, some of the more striking features by which 

 particular bones of certain groups may be recognized. While 

 on this subject, attention may, however, be directed to the 

 imperfection of all collections of avian osteology, the best 

 of them only having skeletons of a certain niimber of species 

 of a larger or smaller number of genera. This deficiency — 

 which is especially noticeable in the Anseres — renders it 

 absolutely impossible to determine specifically a considerable 

 number of bird-bones obtained from the British Pleistocene 

 deposits ; and this impossibility will continue until our 

 national collection obtains skeletons of all the larger birds, 

 not only of the British Isles, but also of the greater part of 

 the Palsearctic region. 



A further difficulty in the study of fossil birds should not 

 be passed over without a brief notice, This difficulty lies in 

 the circumstance that the osteological differences by which 

 the " long-bones " of most of the groups of existing birds 

 are separated from one another are so slight and trivial that 

 when we come to extinct genera it is frequently well-nigh 

 impossible to determine how much value we should attach to 

 the differences we may observe in these bones, in regard to 

 the affinities of their owners to existing types. 



