the Fossil Jaws of Stonesfield. 649 



that the roots of the teeth are enveloped on all sides by the 

 osseous substance. 



Thus we might already, if we had only this piece of the 

 Stonesfield fossil, assure ourselves that it had not belonged to 

 an insectivorous mammal, either placental or marsupial, at 

 which conclusion we had long since arrived with regard to 

 the fragment submitted to our examination by M. Brochant 

 de Villiers. But we have yet to examine the second frag- 

 ment, the basis of the Did. Bucklandii of Mr. Broderip. And 

 here, we do not deny that the task is more difficult ; the more 

 so that we have as yet only figures, which are always insuffi- 

 cient when they are not accompanied by a detailed descrip- 

 tion. 



We shall begin by remarking that this second fragment, 

 when compared with the first, appears so widely different in 

 its general form, and especially in the boat-like curve of its 

 horizontal ramus, in the form of the ascending branch depriv- 

 ed of the angular process, and especially in the dental 

 system, in which we have clearly distinguished three or four 

 incisors, one canine, and seven molars, differing both in form 

 and disposition, — that Mr. Broderip has not scrupled to ex- 

 press an opinion that his Did. Bucklandii could not be ad- 

 mitted even into the same genus as Did. Prevostii ; so that 

 even although we should arrive at proofs that the latter is not 

 a placental or marsupial quadruped, this would be no argu- 

 ment for extending the same conclusion to the former. Let 

 us then see how we may compare the Did. Bucklandii with 

 the two recent generic forms described above. 



Without doubt we cannot deny that in its general aspect as 

 well as in the form and proportion of the two principal parts 

 of the fossil jaw, there is a marked resemblance to that of the 

 Did. Virginiana for example, especially if we suppose that 

 the hooked process of the latter would not be apparent in 

 consequence of its being concealed by the matrix ; at the same 

 time it bears but a very slight degree of resemblance to the 

 Did. Prevostii. We ought however to observe that the con- 

 dyle is rounded, and lies in the prolongation of the dental 

 line, as in the Did. Prevostii; and that in the opossums, on 

 the contrary, the condyle is always more or less transverse, 

 and constantly observed a considerable distance above this 

 line. We should also remark that throughout the whole ex- 

 tent of the horizontal ramus, there appears to be no trace of 

 the foramina in the chin, existing in all the other opossums, 

 which would lead us to think that they had no dental canal ; 

 another point of resemblance to the Did. Prevostii. 



With respect to the dental system, confining ourselves to 



