FOSSIL MAMMALIA FROM THE STONESFTELD SLATE. 423 



(10 mm.) in both cases. Measuring now the space occupied by 

 the eight posterior teeth in the York specimen (including the 

 gap as one tooth), we find that it is the same as in the others. 

 There cau, therefore, be little doubt that the missing tooth was 

 a premolar, the fourth. Returning to the first Oxford speci- 

 men — in front of the three premolars is a space with two 

 sockets, which were evidently occupied by the first premolar, 

 still present in the York jaw. In front of the first premolar 

 we have a region which must be carefully compared in both 

 fossils. As this region in the York specimen is broad and flat, 

 and cannot well be seen from the side, I have given a figure of 

 it more from above (PI. 26, fig. 5 a). The new and only 

 incisor present appears to be the fourth, and three sockets are 

 visible in front of it. Between the incisor and the first pre- 

 molar are two large sockets, somewhat difficult to account for. 

 If the first of these represents a missing canine, and the second 

 a small premolar, we would have one more post-canine tooth 

 in this jaw than in the Oxford specimen (see above). On the 

 other hand, if they both belong to a large double-fanged canine,^ 

 we would then apparently have only three incisors in the Oxford 

 jaw, assuming that here also the canine occupied two sockets.^ 

 On examining the latter specimen closely it is seen that the 

 anterior extremity of the jaw is broken ; moreover the distance 

 from the extremity to the second premolar in the York Am- 

 philestes is 2 mm. longer than in the Oxford specimen. There 

 is, then, no great difficulty in supposing that in the latter the 

 first incisor has been broken away. 



Provisionally the formula of Amphilestes Broderipii 

 may therefore be written i. 4, c. 1, pm. 4, m. 5. 



As for the systematic position of these Stonesfield fossils, 

 the remains are too scanty to allow us to form any very 

 definite opinion. Owen considered Phascolotherium to be 



' Double-fanged canines are not uncommon amongst Mesozoic Mammalia. 



- It is to be noticed that in both the jaws these sockets touch one another, 

 whilst there is a small space on either side of them. Should the York fossil 

 prove to have possessed ten teeth behind a single-fanged canine, it would 

 have to be separated from the Oxford specimens. 



