GEOLOGICAL DISTRIBUTION 



much alike. The molars approximate to the type of those of 

 Triconodon, but the anterior and posterior cones are relatively 

 smaller. Like that of the last-named genus, the mandible of 



Fio. 29. Inner view of the right ramus of the mandible of Phascolotherium bucklandi ; 

 from the Stonesfield Slate. The outline shows the natural size, i, Incisors (one missing) ; c, 

 canine ; p, premolars ; m, molars. The mylohyoid groove is seen near the lower border. (After 

 Owen.) 



Phascolotherium is remarkable for the extremely low position of 

 its articular condyle. In Amphilestes (Fig. 30) of the Stonesfield 

 Slate the molars appear to be of the same general type as those 

 of Phascolotherium, but are more numerous, although their exact 

 number cannot be determined. A somewhat different type 

 of lower molar is displayed by the genus Amblotherium, of the 

 Dorsetshire Purbeck, to which Amphitherium of the Stonesfield Slate 

 was probably allied. This type of tooth is shown in Fig. 4 (8, 9, 

 12) p. 31, and, as there stated, represents that modification of the 

 tritubercular type known as the tubercular sectorial. The three 

 primitive tritubercular cusps form what is known as the blade of 



the tooth, behind which 

 there is the talon or 

 hypocone. A similar 

 form of molar occurs 

 in the existing Opos- 

 sums and Bandicoots. 

 The number of lower 



Fio. 30. Reversed inner view of the left ramus of the . . 



mandible of Amphilestes broderipi; from the Stonesfield teeth m AmOiOtfienum 



Slate. Twice natural size. The restoration of the anterior is i 4, C 1, _p 4, WJ 



teeth is conjectural, and the condyle is placed too high. ^,_g ^'umerOUS allied 

 (After Owen.) 



types, such as Achyro- 



don and Dryolestes occur in the Upper Jurassic of Europe or the 

 United States, while from only one side of the jaw being exposed 

 in each case so-called genera like Stylodon and Stylacodon have been 

 formed upon specimens showing the opposite side to that which 

 is exposed in the types of Amblotherium and Amphitlwrium. The 



