GLIRES OF THE SANTA CRUZ BEDS. 411 



rounded cranium of Loncheres and Echimys. The supraorbital ridges of 

 the frontals are not extended so far backward as in Stichomys and there 

 appears to be no postorbital process ; the forehead is nearly flat, the sinuses 

 causing but slight eminences. The lachrymal is extremely small, as much 

 reduced as in the modern genera named ; the infraorbital foramen has no 

 separate division for the nerve. The rostrum is relatively longer than in 

 Loncheres and its ventral surface is more raised above the level of the hard 

 palate. The interdental portion of the palate is quite short, owing to the 

 extension of the posterior nares, which make a deep, V-shaped incision, 

 with front border almost opposite the middle of m^, thus resembling 

 Echimys rather than Loncheres. 



The mandibles are all incomplete, lacking the coronoid, condyle and 

 angle ; the masseteric crest is prominent and the fossa is deeper than in 

 Stichomys. In some individuals enough of the ascending ramus is pre- 

 served to show that the coronoid was better developed than in Echimys 

 and Loncheres, and that it was set farther back, hardly concealing m^ ; so 

 far as it is preserved, its ventral border is rounded, not flattened, and the 

 pterygoid cre.st, if present, cannot have been so developed as in the last- 

 named recent genera. As compared with that of Stichomys, the ascend- 

 ing ramus is less erect, more inclined backward. 



Relationships. It is evident that this genus is nearly allied to the 

 existing members of the subfamily, but, from the complexity of the denti- 

 tion, it seems unlikely that it was directly ancestral to any of them. 

 Materials are, however, lacking for a definite decision of this latter question. 



SPANIOMYS RIPARIUS Ameghino. 



(Plate LXV, Figs. 22, 23.) 



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



The typical species is distinguished by somewhat larger size, which is 

 about equal to that of Echimys cayennensis, the length of the lower grind- 

 ing series varying from 10.5 to 13 mm. in length, and in most individuals is 

 about 1 2 mm. The external columns of all these teeth are undivided. In 

 the subjoined table the measurements of the upper teeth and skull are 

 from an American Museum specimen, No. 9,529. 



MEASUREMENTS. 



Upper dentition, length 025 Lower incisor, width 0015 



" " " pA-mi 012 " " thickness 002 



