The Mylagaulid.* — Riggs. 



185 



premolar considerably enlarged, though the crown is little elon- 

 gate antero-posteriorly. The third molar is retained, but is 

 somewhat smaller than the second, and short roots are present 

 throughout. Cope describes the mandibular dentition as fol- 

 lows:* " The crowns of the inferior molars, in the unworn con- 

 dition, terminate in two crescents; that is, in elevated, anterior, 

 external and posterior borders, with a transverse ridge equally 

 dividing the space thus marked out and joining the notch in the 

 external crest. This pattern resembles somewhat that of Anchi- 

 theriiim. The first inferior molar (premolar) differs from the 

 others in its superior size and its having the crescents more 

 widely separated by a deeper external emargination. On attri- 

 tion the spaces bounded by the enamel crests are enclosed 

 by the junction of the extremities of these crests on the 

 inner side of the crown. Further attrition results in three 

 lakes within the crown and one notch of the external bor- 

 der and two notches of the internal border. The anterior 

 molar has two lakes in its posterior area and one large one 

 in its anterior area. In old teeth there are successively one 

 and no lakes left to interrupt the dentine. The inferior incisor 

 has a wide shallow groove or concavity on its external face." 



(a) Lower dentition of Mesogaulus X 2. (b) The same of Protogaulus (Mettiscomys, Cope) X 4. 

 (c) Upper dentition of Hystrix refassa X 2. 



From this the affinities with Mesogaulus at once appear. In 

 that genus the lateral emargination of the premolar has almost 

 disappeared, and the cleft is represented by the deeper middle 

 fossette. The large anterior lake described in Proiogaulus is 

 replaced by a smaller one in the later form; the deep postero-in- 



♦Copes Tertiary Vertebra, p. 828. 



