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PART II.— 0/ the Phascolotherium. 

 [Read December 19th, 1838.] 



Plate VI. 



If the question of the existence of the remains of animals so highly organized as 

 Mammalia, in the Stonesfield oohte, depended only on the evidence afforded by 

 the half-jaws of the Thylacotherium described at a previous Meeting of the Geolo- 

 gical Society, that evidence, I have contended, is amply sufficient to enable the ana- 

 tomist to answer that question in the affirmative. 



The remains of the split condjdes in these fossils demonstrate their original con- 

 vex form, — a form which is diametrically opposite to that which characterizes the 

 same part in all Reptiles, and, indeed, in all Ovipara. The size, the figure, and 

 the position of the coronoid process are such as have never yet been witnessed 

 in any other than a zoophagous mammal, with a temporal muscle sufficiently de- 

 veloped to demand so extensive an attachment for the purpose of working a 

 destructive carnivorous jaw. 



The teeth are composed of dense ivory, with crowns covered with a thick coat 

 of enamel ; they are everywhere distinct from the substance of the jaw, and those 

 of the molar series have two fangs, deeply imbedded in distinct sockets. These 

 teeth are, moreover, of three kinds : the hinder ones are bristled with five cusps, 

 of which four seem to have been placed in pairs transversely across the crown of 

 the tooth. The anterior ones present a very different form, and have but two or 

 three cusps in the same plane ; the four anterior teeth were simple, and each with 

 a single fang. Now these particulars have never yet been found united in the 

 teeth of any other than a zoophagous mammiferous quadruped. The general form 

 of the jaw corresponds with the more essential indications of its mammiferous na- 

 ture just described. 



The Thylacotherium being thus established in its true position as regards the 

 primary divisions of the Vertebrate sub-kingdom, there next remained to be de- 

 tected such secondary characters as might reveal the affinities of the fossil to 

 some of the minor groups of the zoophagous and insectivorous Mammalia ; and 

 such seemed to be indicated by the fractured angle of the jaw. But the evidence 

 that may be drawn from this appearance is not so clear and convincing as that 

 which relates to the first and main argument. 



Many naturalists and anatomists may concede the mammiferous character of the 

 Thylacotherium, but may require further evidence in proof of its marsupial nature. 



