472 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



loss of the accessory enamel folds, reducing the crown to two simple 

 prisms. Luaiitlins, a genus from the Patagonian beds, in which the grind- 

 ing teeth are all rooted and the accessory folds are much deeper vertically 

 than in Eocardia, nearly or quite represents the common stock whence all 

 the existing members of the Caviidce have been derived ; its tooth-pattern 

 shows that already in Eocardia the accessory folds were in process of dis- 

 appearance. 



Synonomy. Ameghino originally referred all the species to the single 

 genus Eocardia ; later ('91, 302) he established four subgenera, Eocardia, 

 Procardia, Dicardia and Tricardia, upon the differences in the form of 

 the lower premolar, and finally he raised these to the rank of genera 

 ("94", 74). As will be shown in a succeeding section, Procardia very 

 unexpectedly proves to be a synonym of Schistomys, while, as already 

 pointed out, the variations, both individual and specific, in the form of p ? 

 are so great and the transitions between the extremes is so complete, that, 

 in my judgment, it is both impracticable and unnecessary to divide the 

 genus. Hedimys was established upon a single tooth, which, I am con- 

 fident, is the milk premolar of Eocardia. 



I have found great difficulty in referring the large number of specimens 

 of Eocardia in the Princeton and New York collections to the species 

 already described, because so few of them agree at all closely with the 

 types and because they connect the supposedly distinct species by such 

 gradual transitions. It will therefore be necessary either to increase 

 largely the number of species, or considerably to reduce the number already 

 named. In view of the demonstrated individual variability, reduction is 

 undoubtedly the proper course. 



EOCARDIA MONTANA Ameghino. 



(Plate LXIX, Figs, i, i.) 



Eocardia montana Amegh. ; Observ. gen. sobre el Orden de los Toxo- 



dontes, etc., La Plata, 1887, p. 65. 

 Dicardia maxima Amegh.; Rev. Argent, de Hist. Nat, T. I, 1891, 



p. 302. 

 Dicardia proxima Amegh. ; Enum. Synopt. des Mamm. Foss. de Pata- 



gonie, 1894, p. 74. 



As this, the type species, was established upon a single tooth, which is 

 insufficient for specific identification, it will be necessary to regard as types 



