AMPHITHERIID^. 273 



M. 2297. Cast of a mandibular ramus with seven cheek-teetli of a 

 species belonging to the present section. The original, 

 which is from the Stonesfield Slate, is preserved in the 

 Museum at Oxford, and is figured by Phillips (with an 

 added molar) in his ' Geology of Oxford and the Yalley 

 of the Thames/ p. 234, diagram No. 79, under the name 

 of AmpJiiiJurium prevosti. There are three premolars and 

 a diastema behind the canine ; the fourth cheek-tooth may 

 be mm. 4. Same Jiistory, 



Section B. — The true molars usually differentiated into a bilobed 



blade (which may have a small inner cusp) and a hind talon ; 



four premolars present in all the English genera of which the 



entire lower dentition is known ; and generally four lower 



incisors. 



Those forms which have an inner cusp to the blade of the lower 



true molars approximate to the Diclelpliyidce. It is probable that 



several of the American genera included by Marsh ^ in his Dryolestidce 



belong to the present section ; JDryolestes ^ itself being apparently 



very close to Amhloiherium. In Asihenodon ^, which Marsh regards 



as connecting Dryolestes with Stylodon, the lower true molars have 



no distinct hind talon. 



Genus AMPHITHERIUM, Blainville^ 

 Syn. Amphigonus, Agassiz ^. 



Thylacot her turn, Valenciennes ® (in parte). 



It is uncertain, owing to the imperfect nature of the type specimen, 

 whether this genus (as restricted by Osborn '^) should be referred to 

 the present or the preceding section ; if, however, No. 36822 be 

 rightly referred to it, it undoubtedly belongs to the present one. 



Amphitherium prevosti, Blainville ^ {ex Cuv. MS.). 

 Syn. Didelphis prevosti, Blainville ^. 



Thylacotherium prevosti, Valenciennes ^°. 



This is now taken as the type species of the genus, and is of minute 

 size '\ 



Hah. Europe (England). 



^ Amer. Journ. ser. 3, vol. xxxiii. p. 334 (1887). 



2 Ibid. pi. ix. fig. 2. 3 Ibid. pi. ix. fig. 7. 

 * Comptes Rendus, vol. vii. p. 417 (1838). 



3 Neiies Jahrb. 1835, p. 185. 



'^ Oomptes Rendus, vol. vii. p. 580 (1838). "^ See note 1, p. 271. 



"^ Comptes Eendus, vol. vii. p. 403 {ISSSy—Didelphys. ^ Loc. cif. 



10 Comptes Eendus, vol. vii. p. 580 (1838). 



11 Originally Fhascolofherium was included. 



PAET V. I 



