450 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



PERIMYS PACIFICUS Ameghino. 

 Perimys pacificus Amegh. ; Enum. Synopt. des Mamm. Foss. de Pata- 



gonie ; 1894, p. 72. 

 Perimys pacificus Amegh. ; Segundo Censo de la Repub. Argent. ; T. I, 



1898, p. 179. 



PERIMYS REFLEXUS Ameghino. 

 Perimys reflexus Amegh. ; Enum. Synopt. des Mamm. Foss. de Pata- 



gonie; 1894, p. 72. 

 Perimys reflexus Amegh. ; Segundo Censo de la Repub. Argent. ; T. I, 



1898, p. 179. 



PERIMYS DIMINUTUS Ameghino. 

 Perimys diminutus Amegh.; Enum. Synopt. des Mamm. Foss. de Pata- 



gonie; 1894, p. 73. 

 Perimys diminutus Amegh. ; Segundo Censo de la Repub. Argent. ; T. I, 



1898, p. 179. 



PROLAGOSTOMUS Ameghino. 



(Plate LXVIII, Figs. 15-19.) 



Prolagostomus Amegh.; Enumeracion sistem., etc.; 1887, p. 11. 

 Lagostomus Amegh. in part ; Contrib. al Conoc. de los Mam. Fos. de la 



Repub. Argent.; 1889, p. 185. 



? Sphceramys Amegh.; Enumeracion sistem., etc.; 1887, p. 13. 

 f Sphceromys Amegh.; Contrib. al Conoc. de los Mam. Fos. de la Repub. 

 Argent; 1889, p. 169. 



This genus is much less abundant and varied than the preceding one 

 and is even less well known, owing to the scanty and fragmentary nature 

 of the material. 



The incisors are relatively narrower and more slender than in Viscac- 

 cia and differ from those of Perimys in having decidedly more convex 

 faces; another difference from the latter genus is in the much greater 

 length of the lower incisor, which extends for nearly or quite the whole 

 length of the molar series. The grinding teeth are composed of oblique 

 laminae in close juxtaposition, very much like those of Viscaccia, but 

 apparently without cement between the laminae, which are separated by a 

 single layer of thin enamel, which, however, is but little thinner than that 

 on the periphery of the tooth ; the laminae are demarcated by a vertical 



