408 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



STICHOMYS PLANUS Ameghino. 

 Stichomys planus Amegh.; Rev. Argent, de Hist. Nat; T. I, 1891, p. 299. 



This species differs from all the other known members of the genus in 

 having incisors with plane faces, as in Adelphomys, but differing from the 

 latter in proportions, which are those of Stichomys, the thickness exceed- 

 ing the width. 



Ameghino has named three other species of Stichomys, founded upon 

 differences of size. ,1 have seen no examples of these species. 



STICHOMYS CONSTANS Ameghino. 



Stichomys constans Amegh. ; Enumeracion sistem., etc.; 1887, p. 10. 

 Stichomys gracilis Amegh.; Rev. Argent, de Hist. Nat.; T. I, 1891, p. 300. 



" The lower incisor has a width of hardly more than i mm. and the 

 four inferior molars occupy a longitudinal space of 9 mm.; the length of 

 the diastema is 3.5 mm. and the height of the horizontal ramus below the 

 first molar [p T ] is 5.5 mm." (Amegh., 89', p. 140.) 



S. gracilis appears to be identical with 5. constans, for, though described 

 as considerably smaller, its dimensions, as given, are almost exactly the 

 same; viz., length p^-m^, 5.8 mm.; depth of jaw below p T , 5.5 mm. 



STICHOMYS DIMINUTUS Ameghino. 

 Stichomys dimimitus Amegh.; Rev. Argent, de Hist. Nat; T. I, 1891, p. 



300. 



"Size considerably less than that of the preceding species \i. e., S. 

 gracilis], the first two lower molars occupy a longitudinal space of only 3 

 mm." (Amegh., loc. cit.] 



ADELPHOMYS Ameghino. 

 Adelphomys Amegh.; Enumeracion sistem., etc., 1887, p. 10. 



Closely allied to Stichomys and having similar grinding teeth, but dis- 

 tinguished by the incisor teeth which have plane faces and in which the 

 width equals or exceeds the thickness, thus reversing the proportions found 

 in the incisors of Stichomys. 



ADELPHOMYS CANDIDUS Ameghino. 



Adelphomys candidus Amegh. ; Enumeracion sistem., etc. ; 1887, p. 10. 

 The typical and somewhat smaller species is distinguished by narrower 



