3 1 8 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



on the tibial side being far larger and resembling a small pisiform in ap- 

 pearance. How far this arrangement is peculiar to Pelecyodon, cannot at 

 present be determined. 



Metatarsal IV is longer and very much more slender than III, but does 

 not exceed the latter in length so much as in Hapalops, the relative 

 lengths of the two bones being more as in Analcimorphus, though IV is 

 far more slender than in the latter and has a narrower proximal end than 

 in either of the genera mentioned. 



Metatarsal V is far shorter and slighter than IV and indeed is much 

 more reduced than in any of the other genera of which the foot-structure 

 has been determined ; the proximal end is broad and thick, but the pro- 

 cess given off from the fibular side is much smaller than in Hapalops and 

 the distal trochlea, though small, retains a prominent carina, which has 

 been lost in the latter genus. 



The phalanges are proportionately longer and lighter than those of 

 Hapalops, and those of the various digits differ much in size ; the ungual 

 phalanx of digit III is of relatively enormous size, much exceeding any of 

 the others, and making this the longest, as it is by far the heaviest digit, 

 despite the shortness of the metatarsal and of the second phalanx. The 

 phalanges of digit IV, which approximately equal those of digit II in 

 length, are very slender, while those of V are greatly reduced. The ung- 

 uals are more slender, decurved and sharply pointed than in Hapalops 

 and the distal cleft is longer and more distinct. 



MEASUREMENTS. 



Metatarsal II, length 026 First phalanx, digit II, length 013 



" " proximal width 014 " " " " proximal width .01 1 



" distal width 012 " thick- 



" " thickness 018 ness. .018 



Metatarsal III, length 023 " " " " distal thickness .013 



" " proximal width 024 First phalanx, digit III, length 016 



" " distal width OI55 " " " " proximal width .013 



" thickness ..... .0205 " " thick- 



Metatarsal IV, length 029 ness. .023 



" " proximal width 009 " " " " distal thickness .017 



" distal width 009 First phalanx, digit IV, length 012 



" " " thickness 012 " " " " proximal width .010 



Metatarsal V, length 025 " " " " thick - 



" " distal width 006 ness. .017 



" thickness 0095 First phalanx, digit V, length 0095 



