GLIRES OF THE SANTA CRUZ BEDS. 457 



found in no other species of the genus, but occurs in several species of 

 Perimys ; the external groove between the laminae, which is unusually 

 deep, thus becomes anterior. The lower incisor is of almost exactly equal 

 width and thickness and is therefore thinner than in P. imperialis. 

 The type specimen was collected by Mr. Hatcher at Killik Aike. 



MEASUREMENTS. 



Length r-p^, inclusive 022 P ? , length (i. e., antero-posterior diam- 



Lower incisor, width 0025 eter) 004 



" " thickness 0025 P T , width (i. e., transverse diameter) ... .002 



PROLAGOSTOMUS AMPLUS Ameghino. 

 Prolagostomus amplus Amegh. ; Hnum. Synopt. des Mamm. Foss. de 



Patagonie; 1894, p. 73. 



Of this species, only the type specimen, a mandibular ramus, is known, 

 but it appears, nevertheless, to be a valid one. The lower grinding series, 

 which measures 12.5 mm. in length, is given a different appearance from 

 that of any of the preceding species by having all the teeth of nearly the 

 same size. 



Ameghino has named two additional species of Prolagostomus, concern- 

 ing which I am not able to add anything to his account. 



PROLAGOSTOMUS LATERALIS Ameghino. 

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



Repub. Argent; 1889, p. 185. 

 Prolagostomus lateralis Amegh. ; 6num. Synopt. des Mamm. Foss. de 



Patagonie; 1894, p. 73. 

 Prolagostomus lateralis Amegh. ; Seg. Censo de la Repiib. Argent. ; T. I, 



1898, p. 179. 



PROLAGOSTOMUS PRIMIGENIUS Ameghino. 

 Lagostoimts primigenius Amegh. ; Contrib. al. Conoc. de los Mam. Fos. 



de la Repub. Argent. ; 1889, p. 186. 

 Prolagostomus primigenius Amegh. ; foium. Synopt. des Mamm. Foss. de 



Patagonie; 1894, p. 73. 

 Prolagostomus primigenius Amegh. ; Seg. Censo de la Repub. Argent. ; 



T. I, 1898, p. 179. 



