10 



" stout " fang which supports " all the plica 1 " of the " four-plicated premolars" of 

 Hy/jsipryunn/.s viur in us, &c., as the anterior one. 1 Prof. Phillips's figure gives a more equal 

 share of the crown to the two supporting fangs. The stouter fang of the premolar of 

 Bypsiprymnua (PI. I, fig. 17), always posterior in position, is impressed by a longitudinal 

 groove. In the mandible of llypsiprymnus minor the front fang is much smaller than the 

 hind one. and the interval relatively much less than in the Rhajtic tooth. 



In sum, the Watchet denticle has two fangs and a crown, and a "well defined 

 cervix " between them ; and so has the premolar of llypsiprymnus . their composition in 

 regard to enamel and dentine is the same. Further than this no point of resemblance can 

 be truly predicated as between the Rhoctic tooth and the premolar of any living form of 

 saltatory herbivorous Marsupial. 



The microlestian denticles are comparable with the molars of Myrmecobius and 

 Plagiaulaas, and with these alone in the Marsupial order. The molars of Myrmecobius 

 form a larger proportion of the entire dental series than do those of Plugiaulax. If these 

 genera were represented by detached fossil teeth, it is, numerically, probable that Playiaulux 

 would be represented by some of its sixteen 2 obliquely ridged carnassials, and Myrmecobius 

 by some of its tuberculate molars. 



Now, the numbers of such minute tubercular molars as have brought to light the 

 former existence of a small-toothed predaceous, probably insectivorous, Marsupial, in 

 times so far back as the Triassic, lead me to surmise that the extinct species more 

 resembled the multidentate Myrmecobius and Amphitherium than the paucidentate 

 Playiaulax. 



The small tooth figured in PI. I, fig. 13, nat. size in outline, closely resembles a 

 mammalian canine, and bears the same proportion to the molars of Microlestes as does the 

 canine to the molars in Myrmecobius. 



b. Oolitic Mammals. 



The geological relations of the bed from which the fossils next to be described have 

 been obtained will be understood by reference to the diagram, fig. 2, of the section 

 at Stonesfield from Fitton's Memoir. 3 



On the side opposite the right hand is marked the depth of the shaft to the horizontal 

 gallery where the "slate" is worked which contains the mammalian fossils ; on the opposite 

 side the strata are numbered in succession as follows : 



1 Op. cit., p. 410. 



2 On the assumption that there were as many premolars in the upper as in the lower jaw of 

 Playiaulax minor. 



3 'Zoological Journal,' loc. cit. 



