THE SUPPOSED FOSSIL DIDELPHIS. 53 



from them impressions in sulphur, very carefully executed, 

 and the casts in plaster were thus procured which are to en- 

 rich the paleontological collection of our Museum. 



M. Valenciennes has also received, through M. Laurillard, 

 a drawing very carefully executed, which appears to me to 

 be that originally sent to M. G. Cuvier by Mr. Phillips, and 

 which was taken from a third half-jaw in the possession of 

 Mr. Sikes. 



So that instead of the two specimens of this curious fossil 

 being, as I imagined, the only ones existing in England, ge- 

 ologists now possess four, including that in Mr. Broderip's 

 collection, and even five, according to the first note of M. 

 Agassiz, without reckoning the fragment in "TEcole des 

 Mines'' which we mentioned in our first "doutes," and which 

 is generally referred to the saurians. 



From an actual examination of the two portions of jaw 

 brought over by Professor Buckland, merely the casts of 

 which have been exhibited to the Academy ; — and from the 

 drawing of that in the collection of Mr. Sikes ; — M. Valen- 

 ciennes returns to M. Cuvier's opinion, that it is a marsupial 

 mammal ; he however thinks, like every one before him, that 

 it must form a distinct genus, to which he assigns another 

 new name ; " mais qu'il choisit assez signicatif pour qu'a lui 

 seul, il formule nettement sa maniere de voir." 



It is also on this side of the question that M. E. Geoffroy 

 de Saint-Hilaire, and M. Dumeril have ranged themselves ; 

 the one without explaining the reasons of his conviction, the 

 other basing his upon the presence of a condyle, and the uni- 

 ty of the jaw. 



Without doubt persons who are little versed in the study 

 of organic structures, and who place too implicit a reliance 

 on perhaps rather a presumptuous assertion, that by the aid of 

 a single bone, or of a simple facette of a bone, the skeleton 

 of an animal can be reconstructed, and consequently its class, 

 order, family, genus, and even species determined, may very 

 probably think it strange that four or five half-jaws, more or 

 less furnished with teeth, should be insufficient to indicate 

 promptly and with certainty to what class the animal to which 

 they belonged should be referred ; but their astonishment 

 would cease if they would in the first place observe that in 

 the present case these jaws are perhaps not one of them en- 

 tire ; that they are not to be fully examined either by our- 

 selves or by the parties to whom they belong, on account of 

 their attachment to the matrix enclosing them, and its ex- 

 treme hardness ; but above all because the assertion above 

 quoted, although it has almost passed into a common phrase, 



