84 THE DESEADO FORMATION OF PATAGONIA 



Argyrohyrax acuticostatus Ameghino 



A. acuticostatus Amegh. 1901, Bol. Acad. Nac. Cienc. Cordoba, t. 16, p. 361. 



This species is described as differing from A. proavus 

 in being somewhat smaller, but I find it about the same 

 size. The specific character is in the teeth being more 

 compressed, and in the anterior vertical margin of the 

 upper molars being developed in the form of a very salient 

 crest. 



Isoproedrium Ameghino 



Proedrium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 623. 

 Proedrium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 431. 

 Isoproedrium, Amegh, 1903, Anal. Soc. Cient. Argen., t. 56, p. 18. 



This genus is based on a toothless mandibular sym- 

 physis of large size, on which the second incisor is indicated 

 as larger than the first. We found one lower jaw, which, 

 though imperfect, confirms the above as a genus and adds 

 the following for generic characters; premolars with a 

 shallow inflexion on the inner and outer sides, the molars 

 with a shallow inner, and a narrow deep outer inflexion, 

 heavy layer of cement on the premolars and molars, 

 enamel reduced on the anterior internal, and the posterior 

 internal corners of at least the premolars. 



Isoproedrium solitarium Ameghino 

 loc. cit. above. 



I have assigned the specimen shown in fig. 51 to this 

 species. Alveoli of the first and second incisors show inc. 



, 7 , r- " 



Fig. 51. Right mandible, dotted line indicated alveolus natural size. 



2 considerably larger than inc. I. About the third incisor 

 and the canine my specimen shows nothing, being broken 



