196 MAKSTTPIALIA. 



ridged, although in the genus Liotomus, Cope 1 , they are smooth ; 

 their number varies from one (Neoplayiaulax) to four (Plagiaulax 

 minor and Ctenacodon) : the lower true molars are two in number, 

 of small size, and marked by one longitudinal groove. The upper 

 true molars of the European and North-American genus Neopla- 



Fig. 30. 



Ptilodus mcdi&vus, Cope. The left ramus of the mandible, from the outer (a). 

 inner (b), and oral (c) aspect ; from the Puerco Eocene of New Mexico. }. 

 (From the ' Amer. Nat.') 



yiaulax have three ridges 2 (fig. 29). The mandible of the closely 

 allied North-American Ptilodus is represented in fig. 30 ; in that 

 genus a minute pnTTs is present, and the other slight characters by 

 which it is distinguished from Neoplagiaulax are mentioned by 

 Lemoine 3 . 



Genus PLAGIAULAX, Falconer 4 . 



Including Plioprion, Cope 3 . 



Dentition : I. 1<H*I>, C.^ , Pm. JL, M.|. The lower premolars 

 are obliquely grooved and ridged, and increase gradually in size from 

 the first to the last (woodcut, fig. 31). The condyle of the mandible 

 (as in Thylacoho} is placed below the level of the alveolar line of the 

 cheek-teeth. 



1 Amer. Nat. vol. xviii. p. 691 (1884), Xeaplagiaulax marshi, Lemoine. 



8 From its resemblance to Bolodon, and the difference of its premolars from 

 those referred by Lemoiiie to the upper jaw of Neoplagiaulax, the writer regards 

 the maxilla figured by Marsh (Amer. Journ. 1887, pi. viii. figs. 2, 3) as C'/cita- 

 codon as probably belonging to the Bolodontidce. 



3 Hull. Soc. Geol. France, ser. 3, vol. xi. p. 271 (1883). 



4 Quart. Journ. Geol. Soc. vol. xiii. p. 2fil (1857). 

 8 Amer. Nat. vol. xviii. p. 691 (1884). 



