306 



University of California Publications. 



\ Geology 



The present discussion includes all the buteonid material per- 

 taining' to species that were evidently larger than Archibuteo 

 ferrugineus. This material forms a series of sixty almost perfect 

 tarsometatarsi. The slight imperfections consist in the main of 

 fractures only, there being almost no corrosion. The surface of 

 the bone is as smooth as in newly macerated specimens and 

 assumes, in cleaning, a beautiful polish with every rugosity and 

 every intermuscular line perfectly distinct. Four specimens of 

 Recent American eagles are at hand for comparison. Aquila is 

 represented by one specimen, a large bird fully adult. Haliaetus 

 is represented by an individual taken at Long Island, N. Y., 

 which belongs to the variety leucocephalus, and also by a speci- 

 men of the Alaskan race alascanus, a large female in the collec- 

 tion of the California Museum of Vertebrate Zoology. The 

 peculiar long-shanked group of South American eagles is repre- 

 sented by a single specimen of Geranoaetus melanoleucus, an 

 adult individual of unknown sex. Various smaller American 

 buteonids are at hand, also four Old World forms from the 

 genera Otogyps, Neophron, Circaetus and Gypaetus. 



Besides the actual specimens named, two casts were available 

 for comparison. These casts were made through the courtesy 

 of Dr. A. Smith- Woodward and represent the tarsometatarsi of 

 Thrasaetus harpya and Morphnus guianensis. They are casts 

 of specimens in the British Museum of Natural History. It is a 

 pleasure here to acknowledge the service rendered by Dr. Smith- 

 Woodward. 



The fossil specimens fall easily into five distinct series, each 

 of which shows a remarkable degree of homogeneity, and each of 

 which unquestionably represents a form specifically distinct. 

 Most of the series are large enough to include all individual varia- 

 tions that could reasonably be expected to occur in the limits of a 

 species as the result of varying age, sex, or individuality. The 

 two largest of these series represent the existing Sonoran species 

 Aquila chrysaetos and Haliaetus leucocephalus. Since, however, 

 a detailed discussion of the tarsometatarsus of these forms was 

 not discovered in the literature upon attacking the present prob- 

 lem, it is hoped that a comparison of the two forms here will not 

 prove superfluous. 



