404 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



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



301. 

 Lomomys insulatus Amegh. ; fenum. Synopt. des Mamm. Foss. de Pata- 



gonie; 1894, p. 69. 



Size a little smaller than Scleromys angustus, the upper grinding series 

 measuring 13.5 mm. in length; the molars diminish gradually in size 

 from m 1 to m-. 



OLENOPSIS Ameghino. 

 Olenopsis Amegh. ; Contrib. al Conoc. Mam. Fos. de la Repub. Argent. ; 



1889, p. 145. 



Of this rare genus I have seen no Santa Cruz examples, but only a cast 

 of the Parana species, O. typicus, which has dp T in place, with p T showing 

 beneath it ; the dental formula is thus p T m . In the unworn state the 

 molars are composed of three transverse and somewhat oblique laminae, 

 of which the middle one is the longest; the folds contain thin deposits 

 of cement. On wear, the enamel folds are isolated from the peripheral 

 enamel and form lakes. 



OLENOPSIS UNCINUS Ameghino. 

 Olenopsis uncinus Amegh. ; Contrib. al Conoc. Mam. Fos. de la Repub. 



Argent; 1889, p. 145. 



Characterized by the broad incisors, which have convex faces, and by 

 the comparative simplicity of m , which is similar in pattern to m T , whereas 

 in the later O. typicus, from the Parana beds, it is more complex. In size, 

 O. uncinus is comparable to Neoreomys australis. 



LONCHERIN^E. 



In addition to the foregoing genera, which are, for the most part, com- 

 paratively large animals, the family was represented in Santa Cruz times 

 by a number of smaller rodents, some of them extremely small, in which 

 the grinding teeth are shorter-crowned and have distinct roots. As yet, 

 these genera are known almost entirely from the teeth, imperfect skulls of 

 Stichomys and Spaniomys only having been found and nothing has been 

 learned of the skeleton. The upper grinding teeth have one internal and 

 two or more external folds of enamel, the number of the latter differing 

 in each genus ; in the lower teeth the pattern is reversed, or it may be 

 somewhat simpler. 



