I4H 



CLASS MAMMALIA. 



are regarded by recent authorities as related to Dolichotis, although 

 formerly placed in the Theridomyidce. The crowns of their molars 

 are vertically divided by enamel-folds into two heart-shaped lobes. 

 Hydrochochozrus — the largest living Rodent — is represented in the 

 Brazilian cave-deposits by a species probably identical with the 

 living Capybara, and also in the Pleistocene of Buenos Ayres by an 

 extinct one estimated to have attained a length of five feet, and by 

 a third (H. magnus) of still larger dimensions. An extinct species 

 has also been obtained from the Pleistocene of South Carolina ; 

 and another from the infra-Pampean deposits of Parana. From the 

 latter deposits other forms supposed to be more or less nearly 

 allied to the existing genus have received the names Cardiatherium, 

 Procardiatherium, Cardioi?iys, and Cardiodon ; the latter name had, 

 however, been previously applied to a Sauropodous Dinosaur, 1 and 

 is therefore inadmissible. 



Family Dasyproctid^:. — In this South and Central American 

 family the number of the cheek-teeth is the same as in the last ; 



and these teeth are also semi- 

 rooted, but their crowns have 

 external and internal enamel- 

 folds (fig. 1292); and the in- 

 cisors are long. The type 

 genus Dasyprocta is repre- 

 sented by numerous forms in 

 the Pleistocene of the Brazilian 

 caves ; while a Cce/ogenys oc- 

 curring in the same deposits 

 is probably identical with the 

 living Paca (C. paca). 



Family Chinchillid^:. — 

 This third family of American 

 Rodents has the same dental 

 formula as the last, but the 

 molars have continuous en- 

 amel - folds extending com- 

 pletely across their crowns, and the hind limbs are much elongated. 

 The genus Lagostomus is represented in the South American Pleisto- 

 cene by the existing Vischaca (Z. trichodactylus), as well as by some 

 extinct forms. Megamys from the infra-Pampean deposits of Pata- 

 gonia and Parana is the largest representative of the order yet 

 known ; its bulk being estimated as equal to that of an Ox. Several 

 species have been described, one of which is the type of Pota- 

 marchus of Dr Burmeister. Allied genera from the South American 



Fig. 1292. — Palatal view of the right upper and 

 lower dentition of Dasyprocta. Recent. America. 

 The tooth in each jaw on the right side of the figure 

 is the premolar. 



See page 11 77. 



