I08 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



posterior line and, though somewhat spaced apart, are yet inserted in an 

 imbricating manner; the two median incisors of the opposite sides are 

 separated by a wider space than any of the others. As already indicated 

 in the description of the family, the first five teeth, from i- to p- inclusive, 

 form a series of similar shape, but gradually increasing in size posteriorly. 

 The crowns are of compressed conical form, with trenchant edges and 

 acute points, and curve inward and slightly backward ; the internal cin- 

 gulum is feebly developed near the anterior and posterior margins. The 

 canine differs from the incisors merely in being somewhat larger. Lydek- 

 ker states ('93, 66) that the upper canine has two roots, but this must 

 be merely an individual abnormality; in all of the numerous specimens 

 that I have examined, this tooth is single-rooted. My observations thus 

 agree with those of Ameghino {'94.^, 281). 



The first premolar is isolated by very short diastemata in front of and 

 behind it and is implanted by a single, heavy root; it resembles the 

 canine in form, but is decidedly larger, especially in antero-posterior 

 diameter, and has a complete internal cingulum. I have seen no per- 

 fectly unworn examples of p- and -, but in the former the composition of 

 the crown is plain, even in much worn specimens of the tooth ; it consists 

 of a single outer lobe, with pointed, cordate external face and a distinct 

 external cingulum, and a single, crescentic inner lobe, which appears to 

 be merely a greatly developed and complete internal cingulum ; at all 

 events, no other internal cingulum is present. The tooth is inserted by 

 two massive roots. Premolar - is larger than p-, but, so far as can be 

 judged from the much worn teeth at my disposal, the crown is composed 

 of the same elements, although the inner crescent is not so regularly 

 developed, being enlarged and broadened at the postero-internal angle, 

 thus giving a more asymmetrical shape to the crown. On the other hand, 

 the fourth premolar is almost molariform ; it has two external, crescentic 

 lobes, which are concave outward, but differs from the molars in having 

 only a single principal internal cusp, the deuterocone. The anterior conule 

 is represented by a ridge, which extends from the deuterocone to the 

 antero-external angle of the crown. In perfectly unworn teeth, this ridge 

 rises to an acute point, separated by a cleft from the deuterocone, but this 

 cleft is obliterated in an early stage of wear and then the ridge appears to 

 be a direct outgrowth from the deuterocone. In front of and behind the 

 deuterocone, the cingulum is much elevated and encloses two large. 



