100 STONESFIELD MAMMALS CHAP. 
Amphilestes has teeth of the same pattern but has more of 
them, the premolars and molars being respectively four and five. 
All these animals had the lower jaw inflected. Whether they 
are all Marsupials or not, it is clear that Phascolotheriwn and 
Amphilestes should be united and placed away from Amphithervum 
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 near Oxford, and examined by 
Buckland, Cuvier, and some of the most eminent naturalists 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 he fresh details of their structure ; 
it is probable therefore that now all that there is to be learnt 
from these specimens has been recorded. 
Amphitherium prevostit was a creature about the size of a Rat. 
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 Richard 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—~ze. 
64 teeth altogether. This is a larger number than we find in any 
existing Marsupial. But asin 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 Myrmecobius ; but not, it should be remarked, 
unlike 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 
1 “On the Fossil Mammalia from the Stonesfield Slate,” Quart. Journ. Micr. 
Set. xxxv. 1894, p. 407. 
2 This groove has been found in the existing Myrmecobius, see p. 154. 
