108 AMERICAN PERMIAN VERTEBRATES 



found more or less dislocated from the other tarsal bones; its 

 outer border, that for articulation with the second tarsale, is 

 thickened and rounded; the upper border, meeting the other in 

 an angle, articulated with the centrale, while the distal border, 

 that between the second tarsale and the metatarsal, is short, 

 thin, and free; the inner upper border is also free, but is longer 

 and thicker. 



In the articulation of the tarsal bones as described and figured, 

 a small space is left at the distal end of the astragalus, between 

 it and the inner tarsalia, which must have been filled in life by a 

 small centrale; but no such bone has been found in the numerous 

 specimens recovered, some of them with the foot in nearly com- 

 plete condition. The bone, if present, must have been thin in 

 front view, rather wide perhaps from side to side. Because of its 

 constant absence in the specimens studied I am convinced, as in 

 the front foot, the bone remained unossified in life, represented, I 

 doubt not, by cartilage. 



The phalangeal formula, as determined beyond peradventure, 

 is typically the primitive one, that of the lizards and rhyncho- 

 cephalians; 2, 3, 4, 5, 4. Of the metatarsals, the first is as broad 

 as long, with a thicker border anteriorly at its proximal end. 

 The next three metatarsals progressively increase in length, the 

 third rather the stoutest of all. They are somewhat imbricated 

 proximally, the dorsal margin overlapping the thinner inner side 

 of the next outer bone. The fifth metatarsal is the most slender, 

 about the length of the second, and is somewhat divergent from 

 the fourth; the position in which it is figured is that shown by 

 several specimens. Of the proximal phalanges the first of the 

 fourth digit is the longest, the lengths decreasing as follows in 

 the others: iv-i, iii-i, v-i, iv-2, ii-i, i-i, iii-2, ii-2, i-2, iii-3, 

 iv-3, v-3, v-4. The claws are long, considerably curved, somewhat 

 flattened, but not very sharply acuminate. That of the third 

 toe is the largest; that of the fifth is small; this is the only bone 

 of the whole foot that has not been found in perfect articulation. 

 The close articulation of the digital bones shows clearly a distinct 

 curvature inward or anteriorlv of the second, third, and fourth 

 toes, and as distinctly outward of the fifth toe; the first must have 



