448 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



PERIMYS PUERASTER Ameghino. 

 Sphiggomys ptteraster Amegh. ; Rev. Argent, de Hist. Nat.; T. I, 1891, 



P- 143- 

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



gonie ; 1894, p. 72. 



Though known only from a single fragment of the mandible, containing 

 the broken bases of the incisor and premolar, this is probably a valid 

 species. It is considerably larger than P. puellus, and the mandible, 

 though with very low horizontal ramus, is much more robust than in that 

 species ; below p T it measures 10 mm. in depth and 9 in thickness. P T> 

 which has an antero-posterior diameter of 6 mm. and a transverse width 

 of 3 mm. and is thus narrower and more elongate than in the preceding 

 species, has its valley turned directly forward. 



PERIMYS /EMULUS Ameghino. 



(Plate LXVIII, Fig. 8.) 



Perimys csmulus Amegh. ; Enum. Synopt. des Mamm. Foss. de Patagonie ; 



1894, p. 72. 



This species also is known only from fragments of the mandible, but is 

 clearly distinguished by its large size, which approximates that of P. 

 onustus and P. impactus, from which it differs in the character of p T . This 

 tooth is of the same form as in P. puellus, with the long diameter coinci- 

 dent with the long axis of the jaw and the valley opening directly forward. 

 The lower incisor is relatively broad and its anterior face is depressed and 

 striate ; ir% has an internal pillar, but m r has not. 



MEASUREMENTS. 



Lower dentition, length r-nij 036 P^, width (i. e. transverse diameter). . . .004 



" " " p^-i% 020 Mj, length 0065 



Lower incisor, width 0045 " width 007 



Pj, length (i. e. antero-posterior diam- 

 eter) 0085 



PERIMYS ZONATUS Ameghino. 



Sphiggomys zonatus Amegh. ; Enumeracion sistem, etc. ; 1887, p. 12. 

 Perimys zonatus Amegh. ; Enum. Synopt. des Mamm. Foss. de Patagonie ; 

 1894, p. 72. 



