'i58 Geological Society : — Anniversary 0/^1839. 



that this line of distinction will not be quite sharp and nnbroken, 

 but that there will be apparent transgressions of the rule, while yet 

 the unity of tlie group is indubitable. Thus the Indian Monitor 

 and the Iguana, though Saurians, violate the second character, 

 having an elevated coronoid process ; but then it is narrow, and this 

 seeming defect in our second character is further remedied by 

 the third ; for in those Saurians there is a depressed space between 

 the condyle and the coronoid process quite different from that which 

 a mammal jaw exhibits. Again, the teeth of Crocodiles, Plesio- 

 saurs, and tiie like, are inserted in distinct sockets ; but tlien tliey 

 have not double fangs. The Basilosaurus was supposed to be a sau- 

 rian with double-fanged teeth, but that exception was disposed of 

 afterwards. And as there are thus saurians which trench upon the 

 characters of mammals, there are mammals in which some of the 

 above characters are wanting : thus the condyle is slightly or not 

 at all convex in the Ruminantia ; there is no elevated coronoid pro- 

 cess in the Edentata; the Dolphin and Porpoise have not multi- 

 cuspid teeth ; the Armadillo has not varied forms of teeth, nor has 

 it double fangs to its teeth, Avhich also the fossil Megatherium has 

 not. Still, upon the whole, the above appears to be the general 

 line of distinction. Even if one or two of the above nine marks 

 were wanting to prove the animal a mammal, still if the great ma- 

 joritv of them were present, our judgment could not but be decided 

 by the preponderance of characters. But if all the above characters 

 of mammals are present, and all those of saurians absent, it seems 

 to be a wanton scepticism to doubt that the animal was really warm- 

 blooded. 



Now it was asserted by Mr Owen, who brought this subject be- 

 fore us, that this is the case ; that all the characters whicli I have 

 enumerated above exist in the Stonesfield jaws. If we satisfy our- 

 selves that this is the case, I do not see how we can avoid assenting 

 to his opinion, — that the animal belonged to the class Mammalia. 



Every such question of classification must resolve itself into two ; 

 that of the value, and that of the existence of the characters. If we 

 assent to Mr. Owen in his view of the former, we are then led to 

 consider the latter. 



M. de Blainville, at least in his first examination, had laboured 

 under tlie disadvantage of forming his judgments from casts and 

 drawings only of the Stonesfield bones. Under tliese circumstances, 

 lie had denied several of the above characters; he had held that the 

 teetli in the Tliylacotherium are uniform ; and that they are con- 

 fiuent with the jaw ; and that the jaw is compound. Tliese state- 

 ments Mr. Owen, resting upon a careful examination of the speci- 

 mens, contradicts. The assertion of the compound nature of the 

 jaw is occasioned by a groove near the lower margin of th(> jaw, 

 which however is not so situated as to represent the saurian sutures, 

 but is completely explained by supposing it to lx> a vjiscular canal, 

 such as exists in the Wombat, Didelphys, Opossum, and similar ani- 

 mals. 



Another specimen, at that time the property of Mr. Broderip, 



