54 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



three roots ; the crown has a single external, cordiform lobe and an in- 

 ternal ridge, which in most of the species is distinctly though imperfectly- 

 divided into anterior and posterior cusps (deutero- and tetartocone), 

 while in Licaphriuin this ridge is not so divided. The third and fourth 

 premolars are nearly molariform and of a pattern which closely resembles 

 those of Diadiaphonis, but the two inner cusps are even less distinctly 

 separated. In certain individuals the posterior conule is absent in p-, 

 while in others it is well defined ; in p- this conule is of variable size, 

 sometimes differing notably on the two sides of the same individual. 

 The difference of these premolars from those of Licaphriuin is quite 

 decided and represents a more advanced stage of development. 



The upper molars also are very like those of Diadiaphorus, but with 

 internal cingulum less prominent, or absent, while externally the cingulum 

 is better defined and is continued down upon the anterior border, making 

 a more distinct anterior style. The inner cusps are well separated, almost 

 as deeply as in the last named genus. The third molar is the smallest 

 of the series and its posterior half is much reduced, having no distinct 

 postero-internal cusp, merely a prominent posterior cingulum. Between 

 the inner cusps of one or more of the molars sometimes appears a pointed 

 cingular tubercle, which is absent in most species, in others minute and 

 variable, while in only one species [P. acre) does it become at all con- 

 spicuous. Ameghino has referred this species to a distinct genus, Hepta- 

 conus, but I think this is attributing too much importance to such a char- 

 acter. The molars are not so broad and heavy as in Licaphritim and the 

 internal cusps are more separate. 



B. Lower Jaw. The median incisor, presumably ia, has a small, 

 chisel-shaped, antero-posteriorly compressed crown, with transverse cutting 

 edge ; the lateral incisor, probably i^, is very much larger and caniniform 

 and is broad antero-posteriorly, very thin transversely, which is its prin- 

 cipal difference from the corresponding tooth of Diadiaphorus. The tusk 

 is less procumbent than in Licaphri7im. The canine follows the lateral 

 incisor after a very short diastema and is separated from px by a some- 

 what longer one ; it is very small and has a compressed, bluntly conical 

 crown. 



The first premolar is relatively a little smaller than in Licaphriuin and 

 resembles that of Diadiaphorus, but is more compressed laterally ; pg is 

 also much as in the latter, but is somewhat higher and more pointed and 



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