EDENTATA OF THE SANTA CRUZ BEDS. 293 



distal ends on nearly the same transverse line. This gives to the whole 

 foot a distinctly different appearance, since there is no such marked con- 

 trast in length and thickness between II and III, on the one hand, and 

 IV and V, on the other. 



The phalanges are preserved only in connection with the three external 

 digits and of these only IV has the ungual. The proximal phalanx is 

 shaped much as in H. longiceps, but the median groove of the distal 

 trochlea is far deeper; this phalanx is heaviest in digit III and very small 

 in V. The second phalanx of digit III is very heavy, much longer than 

 in the last named species and has a much more extensive and more deeply 

 grooved distal trochlea, which describes more than a semicircle and 

 projects freely in front of and behind the shaft ; in digit IV this phalanx 

 is longer and much more slender, while in digit V it is of similar shape, 

 but very much smaller, the first and second phalanges together being 

 hardly longer than the proximal one alone of digit IV. Unfortunately, 

 the only ungual phalanx preserved, that of digit IV, is not represented in 

 the type of H. longiceps ; however, in the latter the ungual of digit II is 

 present and it may be assumed that that of IV was not very different. 

 In A. giganteus the ungual of IV is considerably longer than the ungual 

 of the second digit in the last named species, and especially the portion 

 distal to the subungual process is more slender and laterally compressed, 

 more decurved and sharply pointed; the subungual process is not so 

 prominent, but longer proximo-distally, extending to the edge of the 

 trochlea. 



MEASUREMENTS. 



Astragalus, length 044 Metatarsal II, length 037 



" width of trochlea 028 " " proximal width 019 



" " distal end 023 " least width of shaft. . . .012 



Calcaneum, width at constriction OI 95 " distal width 015 



Navicular, length on tibial side 014 Metatarsal III, length 029 



" " " fibular side 004 " " proximal width 024 



width 026 " " least width of shaft .. .017 



" thickness 029 " distal width 0085 



Metatarsus, width of proximal end . . .068 Metatarsal IV, length 034 



Digit IV, length 125 " " proximal width 014 



Metatarsal I, length 022 " " " thickness. . . .020 



" " proximal width 008 " least width of shaft. . . .on 



" " thickness 019 " distal width 0135 



" distal width 009 Metatarsal V, length 034 



" " thickness 018 " " proximal width ?.oi6 



