GLIRES OF THE SANTA CRUZ BEDS. 403 



To this species Ameghino refers an imperfect skull and a mandible, 

 which apparently belong to different individuals, without indicating either 

 as the type. The skull is larger and more robust than that of S. angustus, 

 though the length of the grinding series is the same, or but little greater ; 

 the incisors also are somewhat flattened. 



MEASUREMENTS. 



Upper dentition, length pA-mi 018 Lower dentition, length p^-m^ 022 



" ml-m^ 013 " " " m T -mj 016 



Upper incisor, width 004 



There remain two interesting, but very incompletely known genera, the 

 position of which within the family is uncertain, though the molar pattern 

 renders probable the reference of them to the Capromyince. These genera 

 differ from all other known Santa Cruz rodents in having but three grind- 

 ing teeth. 



LOMOMYS Ameghino. 



Lomomys Amegh. ; Rev. Argent, de Hist. Nat; T. I, 1891, p. 301. 

 Neoreomys Amegh. ; in part. 



From the position of the upper teeth in the jaw and their relation to 

 the posterior nares and to the zygomatic process of the maxillary, it is 

 probable that the dental formula should be written p m. The molar 

 pattern resembles that of Scleromys, with two principal enamel folds, an 

 anterior one from the inner side and a posterior one from the outer side, 

 with a minute enamel lake lying behind the latter. In the unworn state 

 m-3. appears to be composed of three transverse laminae. The two dental 

 series pursue an almost parallel course, without marked anterior con- 

 vergence. 



The hard palate, which is of nearly uniform width, is short and antero- 

 posteriorly convex, rising steeply opposite m 1 ; the posterior palatine for- 

 amina are in the palatine bones. 



The only known species is 



LOMOMYS INSULATUS Ameghino. 



(Plate LXV, Fig. 27.) 



Neoreomys insulatus Amegh.; Contrib. al Conoc. Mam. Fos. de la Repub. 

 Argent; 1889, p. 138. 



