14 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



metacone, enclosing a deep fossa with the posterior conule. The cingu- 

 lum varies somewhat in development, but is always quite prominent on 

 the antero-internal and inner sides, enclosing shallow fossae before and 

 behind the protocone, and ending upon the hypocone. 



When in an advanced state of wear, the molar-pattern has quite a dif- 

 ferent appearance ; an anterior, oblique, transverse crest, or protoloph, is 

 formed by the protocone and anterior conule, which become connate with 

 the paracone, and the posterior conule is confluent with the metacone, 

 from which it forms a projection. Thus there is produced a certain simi- 

 larity to the molar-pattern of Palcsotherium, to which attention has often 

 been called, but the absence of the posterior crest (metaloph) and the 

 consequent irregular, S-shape of the valley are significant differences. 



The third molar is the smallest of the series and is made asymmetrical 

 by the reduction of the posterior half of the crown ; the metacone is con- 

 siderably smaller than the paracone and the hypocone is extremely small. 

 All of the grinding teeth are closely appressed, so that the postero-external 

 angle of each tooth actually notches the .tooth behind it. 



B. Lower Jaw. The median incisor (i2-) is a very small, simple and 

 subconical tooth, which, to all appearance, can have been of little or no 

 functional importance, for even in very old animals it shows hardly any 

 sign of wear. The lateral incisor (is-) is tusk-like, somewhat thinner and 

 more compressed than the upper tusk, behind which it bites. The canine 

 is very small and simple. 



The first lower premolar (px) is much the smallest of the series and is 

 inserted by a single root ; the crown is simple and of elongate, compressed- 

 conical shape, with cingulum well defined on the inner, but not on the 

 outer side. The second premolar is of similar shape, but is very much 

 larger and is carried upon two roots ; the cingulum is prominent both in- 

 ternally and externally and on the inner side are two low ridges, enclosing 

 shallow fossae, of which the posterior is much the larger and deeper. The 

 third and fourth premolars are molariform, but ps has a minute pillar on 

 the inner side of the front end of the anterior crescent, and p^ has a similar 

 pillar on the hinder end of the posterior crescent. 



The lower molars are much like those of Anoplothermni, PalcBotherium 

 and Titanotherium and are composed of two crescents, without accessory 

 cusps or styles, but with prominent cingulum ; m-s has no talon or unpaired 

 lobe. In entirely unworn teeth, minute vestiges of the postero-internal 

 pillar may sometimes be observed in m2^ and 3. 



