1911] 



Miller: Eagle Tarsi from Bancho La Brea. 



315 



Dimensions of the Type Specimen 



Tarsometatarsals — 



Length over all 



Length to papilla of tibialis anticus ... 



Transverse diameter of head 



Transverse diameter through trochleae 



Least transverse diameter of shaft 



Greatest sagittal diameter of head 



109. mm. 



26. 



20. 



22.5 



10. 



17.3 



GERANOAETUS FRAGILIS, n. sp. 



Type specimen no. 12757, Univ. Calif. Col. Vert. Palae., tar- 

 sometatarsus. When compared with G. melanoleucus this form 

 exhibits the following characters : Length equal to G. melanoleu- 

 cus, but width much less; position of papilla of tibialis anticus 

 much higher; proximal depression and proximal foramina much 

 the same. Antero-exterior ridge of shaft sharper ; inner hypo- 

 tarsal ridge placed much nearer center of the shaft, the hypo- 

 tarsal ridges very close together and the intervening furrow 

 more than a semicircle in cross-section. 



In size the closest resemblance of this species is to Geranoaetus grin- 

 nelli. It is, however, distinguishable by its greater slenderness, the higher 

 position of the papilla of the tibialis anticus, the greater distance between 

 the- proximal foramina, the shorter supratendinal bridge, and the elonga- 

 tion of the papilla at the inner end of this bridge into a vertical crest 

 which merges upward into the margin of the proximal articular surface. 

 On the posterior side the inner hypotarsal ridge is not prolonged down- 

 ward along the shaft, but is stopped abruptly by the posterior opening 

 of the internal proximal foramen. This foramen in each of the four speci- 

 mens of the series opens posteriorly exactly at the lower limit of the hypo- 

 tarsal ridge, whereas in the nine specimens of Geranoaetus grinnelli, the 

 base of the inner ridge extends down the shaft beyond the foramen and on 

 its inner side. 



This species is represented by a series of four tarsometatarsi 

 which display a remarkable degree of uniformity. The slight 

 variation in heaviness is ascribed to difference in sex. The 

 extreme of specialization among the larger buteonids toward 

 an elongate and slender tarsometatarsus seems here to have been 

 reached. The transverse diameter of the head, foot and shaft are 

 almost exactly equal to the corresponding dimensions in Archi- 

 buteo ferrugineus, while the length exceeds that of Aquila and 

 equals that of Geranoaetus melanoleucus. The relation of power 

 arm to weight arm in the flexure of the tarsal joint is 16.6%, a 



