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University of California Publications in Geology t VoL - 1(1 



A navicular (fig. 20) of the left foot is somewhat larger than the 

 corresponding bone in the specimen of A. simum from Potter Creek 

 Cave. The differences in the form of the element are not large. 

 Although the navicular in no. 22362 is noticeably broader than the 

 corresponding tarsal element in Arctotherium from Potter Creek Cave, 

 it lias approximately the same depth. In the Pliocene specimen 

 the facet for the astragalus is not as deeply concave as that in Arcto- 

 therium. The ventral portion of the articulating surface for the 

 cuboid is larger and truncates the lateral margin more acutely than 

 in the latter genus. Along the external border of the navicular this 

 surface is less extensive than in Ursus. The union of the median 

 and ventral borders is less distinctly rounded than in A. simum. The 

 distal articulating surface is obscurely divided for the cuneiform 

 elements. The ventral tubercle is large. 



The cuboid 'figs. 21a to 21c) possesses a long inner side and 

 approaches more nearly a euboidal form than does the corresponding 

 element in the Recent Ursus. The cuboid of the Pleistocene Arcto- 

 l/n mi in from Potter Creek Cave is in this regard intermediate between 

 that of no. 22362 and Ursus. In contrast to Arctotherium the angle 

 between the dorsal plane and the plane of the metatarsal facet in the 

 Pliocene cuboid is less acute. 



The larger cuboid facet for the navicular is subtriangular. It is 

 separated from an inner facet for the astragalus by a right angle, and 

 is directed decidedly toward the ventral side. In Arctotherium and in 

 Ursus this surface is directed more toward the inner side of the cuboid 

 and is separated from the astragalar facet by an obtuse angle. The 

 distal end of the boundary between the navicular and astragalar facets 

 is truncated by a very small articulating surface also for the navicular, 

 The latter has a greater dorso-ventral extent in Arctotherium . 



The concave cuboid facet for the astragalus differs in its greater 

 size and rectangular form from that in Arctotherium and in the Recent 

 Ursus. Distal to this facet and widely separated from it is a large and 

 flat articulating surface for the external cuneiform. In A. simum 

 this surface is broadly confluent with the navicular facet. It is situated 

 farther to the ventral side in no. 22362 than in the cuboid of A. simum. 

 Only a single facet articulates with the external cuneiform at the 

 distal margin of the cuboid. 



The metatarsal facet of the cuboid is triangular and relatively 

 smaller than in Arctotherium. On the ventral side of the cuboid the 

 transverse ridge is situated farther proximally, especially toward the 



