GLIRES OF THE SANTA CRUZ BEDS. 409 



incisors and more slender horizontal ramus of the mandible. The lower 

 grinding series is 14 mm. long and the lower incisor is 2 mm. wide. 



ADELPHOMYS EXIMIUS Ameghino. 

 Adelphomys eximius Amegh. ; Enum. Synopt. des Mamm. Foss. de Pata- 



gonie; 1894, p. 69. 



This is a rather more robust animal than the preceding one, with heavier 

 lower jaw and broader incisors, which measure 2.5 mm. in width. 



GYRIGNOPHUS Ameghino. . 



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



The original description of this genus reads as follows : "Of characters 

 intermediate between Spaniomys and Stichomys. The first two lower 

 molars \i. e., p T and mij have three folds on the inner side and the last 

 two only two." On making an enlargement of the photograph which I 

 took of the type specimen it appeared that m^ also had three internal 

 folds, the median one of which is much narrower and shallower than the 

 others, and is filled with matrix, so as to be very difficult to see. The 

 tooth has therefore been figured (PI. LXV, fig. 25) with three such folds, 

 though I do not feel entirely confident that such an interpretation is cor- 

 rect. At all events, the pattern of m^ is sufficiently different from that of 

 Spaniomys to justify the generic distinction. (Cf. figs. 23 and 25, PI. 

 LXV.) It is further evident that m^ is only beginning to take on the full 

 complication of the preceding teeth. 



The only species yet known is 



GYRIGNOPHUS COMPLICATUS Ameghino. 



(Plate LXV, Fig. 25.) 



Gyrignophus complicatus Amegh. ; Rev. Argent, de Hist. Nat. ; T. I, 1891, 



P- 300. 



This is a very small animal, about equal to Stichomys constans in size. 

 The series of inferior grinding teeth is 10 mm. in length and the depth 

 of the horizontal ramus below p r is 6 mm. 



SPANIOMYS Ameghino. 



(Plate LXV, Figs. 22-24.) 

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



