THE SUPPOSED FOSSIL DIDELPHIS. 55 



Kient in the hands of M. Valenciennes, who unfortunately did 

 not consider himself at liberty to lend it to him, — M. de Blain- 

 ville thinks that the palmated, five-lobed form of the posterior 

 molars would alone be sufficient to negative all approach to 

 the didelphs, and even to the Mammalia. 



Insomuch that M. de Blainville reviewing the reasons up- 

 on which M. Valenciennes bases his opinion, namely, — the 

 existence of a condyle, the presence of which upon either of 

 the impressions cited M. de Blainville positively denies, — 

 the form of the teeth, which certainly have no relation in num- 

 ber, disposition, or shape, to those of the Didelphis murina, 

 any more than to those of any other known mammal, although 

 they support themselves upon what M. Agassiz has said of 

 the teeth having five points, disposed as in the Insectivora, 

 which is not the case, as we have seen in the note given li- 

 terally above ; the aspect of the ascending ramus, which, in 

 both specimens is mutilated, and has only left its impression, 

 indicating a kind of very slender plate, slightly convex ex- 

 ternally, and concave within ; —the symphysis, which exists 

 only in appearance ; — the opening of the dental canal, of 

 which also he denies the existence, since the jaw is seen on 

 the outer side, and which had neither the form nor the posi- 

 tion of that of the Didelphis, nor even of other Mammalia ; 

 — the prolongation of the angular process, which has nothing 

 in its shape to remind us of that of the didelphs, and which 

 rather brings to our recollection that of certain fishes ; — and 

 finally, the compound structure of the jaw, which might very 

 well be no longer distinctly visible in a fragment so long ago 

 fossilized, and yet have existed ; and of which, it appears to 

 him there are left some traces in the lower marginal ridge still 

 visible in the two specimens, and in the projection where it 

 commences. 



M. de Blainville then finds himself compelled to pause, at 

 least until fresh evidence be produced; in the conviction that 

 the portions of fossil jaws found at Stonesfield, certainly do 

 not belong to a marsupial, — and probably not to a placental 

 mammal, either insectivorous or amphibious ; and that con- 

 sequently it is more likely that the animal may have been 

 oviparous. 



As to the doubt which he has just formed by analogy with 

 what is known of the Basilosaurus, a large fossil reptile of 

 America, the teeth of which display the peculiarity of posses- 

 sing a double root, — that this might be an animal of the sau- 

 rian order, — M. de Blainville says that if M. Agassiz, who 

 has studied fossil fish much more even than himself, had not 

 decidedly given his opinion against all approach to fishes, he 



