460 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



family ; in the abraded state it has one deep external and two much shal- 

 lower internal enamel folds, which divide the tooth into two principal 

 lobes, in the anterior one of which is a minute enamel lake. The milk 

 premolar is much more complex. The incisor is short and extends only 

 to the premolar. The masseteric crest is very prominent. 



SPHODROMYS SCALARIS Ameghino. 



(Plate LXVIII, Fig. 21.) 



Sphodromys scalaris Amegh. ; Enumeration sistem., etc.; 1887, p. 13. 



The extremely small size of the animal is the only specific character 

 that presents itself. Length from p T to r%, inclusive, 7 mm. 



CAYIID&. 



(Eocardidce Amegh.) 

 EOCARDIA Ameghino. 



(Plates LXVIII, Figs. 23-25; LXIX, i-io, 17; LXXI. 



Eocardia Amegh. ; Observ. gen. sobre el Orden de los Toxodontes, etc. ; 



La Plata, 1887, p. 65. 

 Dicardia Amegh. (subgenus) ; Revist. Argent, de Hist. Nat. ; T. I, 1891, 



p. 302. 

 Dicardia Amegh. (genus) ; Enum. Synopt. des Mamm. Foss. de Pata- 



gonie; 1894, p. 74. 

 Tricardia Amegh. (subgenus) ; Revist. Argent, de Hist. Nat. ; T. I, 



1891, p. 302. 

 Tricardia Amegh. (genus) ; Enum. Synopt. des Mamm. Foss. de Pata- 



gonie; 1894, p. 74. 



Hedymys Amegh. ; Enumeracion sistem., etc.; 1887, p. 14. 

 Hedimys Amegh. ; Enum. Synopt. des Mamm. Foss. de Patagonie ; 



1894, p. 74. 



This is one of the most abundant and characteristic of Santa Cruz 

 rodents, of which nearly the entire skeleton is represented in the Prince- 

 ton collection, so that it is possible to make satisfactory comparisons with 

 other contemporary and with recent genera. 



The dentition closely resembles that of Dolichotis, though in several 

 respects that of the Santa Cruz genus is much more primitive. The in- 



