lOO STONESFIELD MAMMALS 



Ampliihstes has teeth of the same pattern luit has more of 

 them, the premolars and mohirs being respectively four and five. 

 All these animals had the lower jaw inflected. Whether they 

 are all Marsupials or not, it is clear that Pliascolotherium and 

 Ampliihstes should be united and placed away from Ainpli itlierium 

 on account of the more primitive form of their teeth. 



We next come to the Trituberculata. 



Among the most celebrated of these remains are a few jaws 

 discovered in the Stonesfield slates hear Oxford, and examined by 

 Buckland, Cuvier, and some of the most eminent natm-alists of the 

 beginning of the last century. These jaws have been lately sub- 

 mitted to a careful re-examination by Mr. Goodrich,^ who has 

 increased our knowledge of the subject by exposing from the 

 rocky matrix in which the jaws lie fresh details of their structure ; 

 it is probable therefore that now all that there is to be learnt 

 from these specimens has been recorded. 



Arnjihitheriuin j^i'evostii was a creature about the size of a Eat. 

 Its jaw was first brought to Dean Buckland about the year 1814, 

 and described six years later. Buckland thought the jaw to be 

 that of an Opossum, an opinion in which Cuvier concurred. The 

 jaw, however, is marked by a groove running along its length, and 

 this groove was regarded by de Blainville as evidence of the com- 

 position of the jaw out of more than one element, which would 

 naturally lead to its being regarded as the jaw of a reptile.^ This 

 species and another named after Sir Eichard Owen have a dental 

 formula which, like that of the Marsupials, is large as compared with 

 that of the Placental mammals ; it runs : I 4, C 1, Pm 5, M 6 — i.e. 

 64 teeth altogether. This is a larger number than we find in any 

 existing Marsupial. But as in Marsupials, and in certain Insectivora 

 also, the angle of the jaw is inflected. These teeth are of the 

 tritubercular pattern with a " heel." They are in fact closely like 

 those of the living MyrmecoMus ; but not, it should be remarked, 

 unhke those of certain Insectivora. 



The Mammals of the Cretaceous Period. — At one time 

 there was a totally inexplicable gap between the Jurassic and 

 the basal Eocene, a series of strata which occupy an enormous 

 expanse of time in the history of the earth having appeared to 



^ "On the Fossil Mammalia from the Stonesfield Slate," Quart. Journ. Micr. 

 Sci. XXXV. 1894, p. 407. 



^ This groove has been found in the existing Mynnecohiits, see p. 154. 



