EDENTATA OF THE SANTA CRUZ BEDS. 179 



ably in length and shape, even in the same genus ; the condyle is set 

 upon a very long, slender neck and this, together with the high coronoid 

 and the very long angular process, gives to this part of the mandible a 

 characteristically trifid appearance. 



The neck is elongate and slender, with small and rather weak vertebrae. 

 The trunk, and especially the thoracic region, is very long and has numer- 

 ous vertebrae, in some cases at least, as many as 25 ; the loins are short and 

 heavy ; the articular processes in the lumbar and posterior thoracic regions 

 are relatively simple, only one additional pair each of pre- and postzy- 

 gapophyses being present. The tail is stout, but not so massive as in 

 the Planopsidce. 



Compared with those of the other two families, the limb-bones are rather 

 slender. The manus has very long, compressed and sharp ungual pha- 

 langes, especially on the median three digits. The femur invariably has a 

 prominent third trochanter. The astragalus is relatively long and narrow, 

 moderately or faintly grooved and rarely shows any tendency for the inner 

 condyle to assume the odontoid shape. The calcaneum has a short sus- 

 tentaculum, the astragalar facet of which presents distally and is nearly 

 parallel to the facet for the cuboid, which is large and circular. The pha- 

 langes are heavier than those of the manus, but the unguals are shorter. 

 There is no apparent reason to doubt that the pes was plantigrade and 

 that the entire plantar surface was applied to the ground, unless the partial 

 displacement of the cuboid to the plantar side of the astragalus should be 

 regarded as such a reason. 



HAPALOPS Ameghino. 



(Plates XXX-XLV.) 



Hapahps Amegh.; Enumeracion sistematica, etc., 1887, p. 22. 

 Eucholceops Amegh., in part; Ibid., p. 21. 

 Xyophorus Amegh.; Ibid., p. 23. 



Parhapalops Amegh.; Rev. Argent, de Hist. Nat, T. I, 1891, p. 318. 

 Pseudhapalops Amegh.; Ibid., p. 319. 

 AmpJiihapalops Amegh. ; Ibid., p. 319. 

 Geronops Amegh.; Ibid., p. 320. 

 Eugeronops Amegh.; Ibid., p. 397. 



Schismotherium Mercerat (non Ameghino) ; Rev. del Museo de La Plata, 

 T. II, 1891, p. 5. 



