76 PATAGONIAN EXPEDITIONS! PALAEONTOLOGY. 



Of the pes (Plate VI, fig. 18) we have the tarsus complete, and all the 

 metatarsals, except metatarsal V, but without phalanges. As in all other 

 parts of the skeleton, there is close resemblance to Zaedyus, with a number 

 of minor differences. The astragalus is relatively narrower and has a more 

 elongate, slender and less depressed neck. In the calcaneum, the tuber 

 is somewhat longer and heavier, with more expanded and club-like proxi- 

 mal end, which has a shallower tendinal sulcus ; the external tubercle near 

 the distal end for the attachment of the lateral ligament is less promi- 

 nent. The accessory, spur-like ossicle, which is so conspicuous in the 

 recent genus, was doubtless present in the fossil, as is indicated by the 

 prominent tubercle which arises from the inner side of the navicular and 

 bears a distinct facet. The ento-cuneiform has a more quadrate shape 

 than in the modern animal, its proximal end not being truncated, which 

 is an indication that the accessory ossicle had a different shape. The meso- 

 and ecto-cuneiforms differ in no tangible fashion from those of Zaedyus. 

 Metatarsal I is somewhat longer than in the latter, while metatarsal II is 

 proportionately more slender, as is also metatarsal III, which is the long- 

 est of the series, metatarsal IV being of nearly the same length as II. 



Tax onomic Position. From the foregoing description, it will be suf- 

 ficiently clear ihat this genus is very closely allied to the recent Zaedyus, 

 for all parts of the skeleton show the closest correspondence between 

 them, with differences of only very minor importance. Systematically, 

 the only difference of generic value is in the carapace, which in the fossil 

 has no scapular buckler, but, except in the hinder part, is formed of mov- 

 able, imbricating bands. There seems to be no reason to doubt that Pro- 

 zaedius is well named, as being the ancestor of Zaedyus. Aside from the 

 rodents, no other instance is known of so close and direct a connection 

 between a recent genus and one of Santa Cruz times. 



PROZAEDIUS EXILIS Ameghino. 



(Plate VI, figs. 1-14.) 



Euphractus exilis Amegh. ; Enumeracion sistematica, etc., 1887, p. 26. 

 Zaedyus exilis Amegh. ; Contrib. al Conoc. de Mam. Fos. de la Repub. 



Argent, 1889, p. 868. 



Prozaedius exilis Amegh. ; Rev. Arg. de Hist. Nat, T. I, 1891, p. 327. 

 Dasypus exilis Lydekker ; Anales del Museo de La Plata, T. Ill, 1894, 



p. 62. 



