1912] Miller: Pacific Coast Avian Palaeontology 63 
assistance extended by him to the author, our knowledge of the 
Hawver Cave deposits has been greatly advanced. To each of 
these persons the author’s sincere thanks are extended. 
SIGNIFICANCE OF OSTEOLOGICAL CHARACTERS IN ORNITHOLOGY 
In a zoological group of such narrow delineation and of such 
great homogeneity as the class Aves, where separation into the 
various systematic divisions is based upon relatively small varia- 
tions and where these variations affect structures not preserved 
for study, a considerable degree of care must be exercised when 
interpreting discoveries of the palaeontologist in terms of modern 
systematic zoology. The difference noticeable to a worker in the 
former field should in many cases be multiplied by a very large 
factor upon their transposal to the latter. Degrees of diver- 
gence which to the palaeontologist seem of no more than specific 
rank might, by the worker in systematie ornithology, having 
also various intricate details of color-pattern or feather struc- 
ture at his disposal, be found correlated with differences of 
more than generic importance. The distinetion upon osteological 
characters of many well-defined species of Recent birds is a 
matter requiring complete skeletons of individuals of known sex; 
even then conclusions are often in question. It is here con- 
ceded as possible under these conditions, and considering the 
fact that most of the fossil specimens are not capable of articula- 
tion, that many of the fossil specimens ascribed to living species 
might, if all characters were determinable, be separated as dis- 
tinct forms. It must be remembered also that within certain 
groups the osteological differences between species is greater than 
in others. The feather of the bird is an epidermal structure 
which reflects with sensitiveness the activities of the animal and 
is plastic as a specific character under the influences of environ- 
mental changes. It is a proper basis of specific distinction, yet 
it is almost never preserved in the fossil state. The tooth of 
the mammal, likewise an epidermal structure and highly repre- 
sentative of the animal’s activities, is a character used in com- 
mon by the palaeontologist and the modern systematist. Zoology 
and palaeontology are then much more nearly upon the same 
