50 



University of California Publications. 



[Geology 



sharp sabres. When the canines are not developed to the dagger- 

 like form for stabbing, the premolar teeth serve a more definite 

 purpose in the destruction of prey, and would be less subject to 

 reduction. 



The view suggested above finds support, in that such evidence 

 as we have indicates that during the deposition of the Middle 

 John Day beds this region was in the main a country of open 

 plains, offering advantages to running types of carnivores, and 

 that during this epoch the Archaelurus-Nimravus type of feline 

 was by far the most common form. 



As might be surmised from the known similarities in cranial 

 and dental characters, the foot structure of Archaelurus shows 

 considerable resemblance to that in the genus Ailurictis of the 

 European Oligocene. As has been shown by Schlosser, 30 meta- 

 tarsal one is greatly reduced in Ailurictis, and particularly the 

 middle metapodials are rather heavy. These characters, as also 

 the unusual elongation of the proximal, external tubercle on 

 metatarsal five, are distinctive features of Archaelurus. The limb 

 structure differs somewhat in the two groups in that metatarsals, 

 two and five are somewhat less reduced in Ailurictis, and the 

 astragalus is stated to show close resemblance to that of Felis, 

 while in Archaelurus this element has a different and quite dis- 

 tinctive form. As far as can be determined, Archaelurus seems, 

 slightly more advanced than Ailurictis in foot structure. 



MEASUREMENTS. 



A. debilis major, No. 2256. 



mm. 



Femur,' 10 anteroposterior diameter of head 



Femur, transverse diameter of shaft near middle 



Femur, transverse diameter of distal end 



Femur, width of rotular face at middle 



Tibia, transverse diameter at distal end 



Tibia, transverse diameter at proximal end 



Tibia, antero-posterior diameter at proximal end 

 Calcaneum, greatest afltero-posterior diameter 



22.8. 



22 



50.5 



18 



33.5, 



48 



52 



67 



30 M. Schlosser. Beitrage zur Palaeont. Oestr-Ung., B. 6, p. 431. 

 40 The shaft of the bone has been shattered in the femur and tibia so that 

 the length could not be accurately determined in this specimen. 



