64 University of California Publications in Geology [VOL. 7 



basis in the determination of mammals than is the case with 

 birds. Recognizing this principle, the author of this paper has 

 proceeded with perhaps more than necessary caution in the an- 

 nouncement of new species, preferring to err on the part of 

 conservatism rather than to confuse the literature of the subject 

 by making assertions which must later be modified ; and there are 

 in the collections studied many specimens regarding which fur- 

 ther knowledge is considered necessary before problems upon 

 which they may throw light can be attacked in more than a 

 speculative way. 



REVIEW OF THE LITERATURE 



Since the epoch-making discoveries by Marsh which added 

 so materially to our conception of the ancestry of birds, con- 

 tributions to knowledge in the field of avian palaeontology have 

 been few as compared with the rapid enlargement of our under- 

 standing of the other vertebrate groups. Bird remains on the 

 Pacific Coast are mainly from Pleistocene strata; thus there is 

 eliminated the probability of shedding much new light upon the 

 ancestry of certain groups in which our interest is so acutely 

 focused, for example the Stereornithes. Discoveries recently 

 made have contributed to science chiefly in two ways, first in 

 giving us an appreciation of the relative antiquity of the main 

 groups into which birds are divided; and, second, in adding to 

 our knowledge of the geographical distribution of these groups. 

 The consideration of geographical distribution is but begun when 

 we record the range of the Recent species. Determination of 

 the factors which have led to such distribution, if we aspire to 

 something better than mere speculation, must look to the record 

 of previous conditions as brought to light through palaeontol- 

 ogical inquiry. 



The fossil-bearing rocks of the Pacific Coast of North 

 America, while rich in the remains of mammals and reptiles, 

 have until recently yielded but little information concerning the 

 avian group. 



In 1878, Cope 1 described three new species of birds from 

 the Equus Beds of Oregon. All three species belong to genera 



i Cope, E. D., Bull. U. S. G. S., Terr., iv, No. 2, May 3, 1878. 



