402 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



broader and more flattened, contracting posteriorly to a short, narrow 

 sagittal area, without trace of a sagittal crest. The palate is distinctly 

 wider and the posterior narial opening conspicuously so, not only pro- 

 portionately, but actually, and is of a somewhat different shape, the front 

 border of the opening being more regularly curved and without median 

 spine. The incisors extend farther into the maxillaries, the preorbital por- 

 tion of which is relatively somewhat longer than in Neoreomys. 



From all the known material, it seems sufficiently evident that Scleromys 

 is closely allied to Neoreomys. Ameghino has suggested ("94", 69) that it 

 is ancestral to Ctenomys, but the character of the teeth seems to forbid 

 such an association, while the skull is of quite a different type. 



SCLEROMYS ANGUSTUS Ameghino. 



(Plate LXV, Figs. 13, 14.) 



Scleromys angustus Amegh. ; Enumeracion sistemat, etc., 1887, p. n. 

 ? Neoreomys limatus Amegh.; Revist. Argent, de Hist. Nat, T. I, 1891, 

 p. 142. 



The type and possibly the only species. It is distinguished by its 

 somewhat smaller size and more slender proportions, and by the more 

 convex faces of the incisor teeth. 



The type of Neoreomys limatus is a mandible with much abraded teeth ; 

 it is apparently referable to the present species, with which it agrees in size. 



In the subjoined table the dimensions of the upper jaw are taken from 

 a palate, with teeth, in the collection of the American Museum of Natural 

 History (No. 9,304) and those of the lower jaw from a specimen in the 



Ameghino collection. 



MEASUREMENTS. 



Upper dentition, length 044 Palate, width at pi 006 



" " " pi-mi 018 " ", "ml 012 



" " " mi-mi 013 Lower dentition, length 035 



Upper incisor, width 004 " " " p^-m^ 020 



" " thickness 0043 " " " m T -nij 013 



SCLEROMYS OSBORNIANUS Ameghino. 



(Plate LXV, Fig. 15.) 



Scleromys osbornianus Amegh., Enum. Synopt. des Mamm. Foss. de Pata- 

 gonie, 1894, p. 69. 



