"204 FOSSIL JAWS FROM STONESFIELD. 



number of its molars, and from every ferine quadruped known at the time 

 when Cuvier formed his opinion respecting the nature of the fossil. This 

 difference in the number of the molar teeth, which Cuvier urged as evidence 

 of the generic distinction of the Stonesfield mammiferous fossils, has since 

 been regarded as one of the proofs of their saurian nature ; but the excep- 

 tions by excess to the number seven, assigned by M. de Blainville to the 

 molar teeth in each ramus of the lower jaw of the insectivorous Mammalia, 

 are well established aud have been long known. The insectivorous chryso- 

 chlore, in the order Feres, has eight molars in each ramus of the lower jaw; 

 the insectivorous armadillos have not fewer ; and in one subgenus (Priodon) 

 there are more than twenty molar teeth on each side of the lower jaw. The 

 dental formula of the carnivorous Cetacea, again, demonstrate the fallacy of 

 the argument against the mammiferous character of the Thylacotherium 

 founded upon the number of its molar teeth. From the occurrence of the 

 above exceptions in recent placental Mammalia, the example of alike excess 

 in the number of molar teeth in the marsupial fossil ought rather to have led 

 to the expectation of the discovery of a similar case among existing marsu- 

 pials; and such an addition to our zoological catalogues has, in fact, been 

 recently made. In the Australian quadruped described by Mr. Waterhouse 

 under the name of Myrmecobius, an approximation towards the dentition 

 of the Thylacotherium is exemplified, not only in the number of the molar 

 teeth, which is nine on each side of the lower jaw in the Myrmecobius, but 

 also in their relative size, structure, and disposition. Lastly, with respect to 

 the dentition, Mr. Owen says it must be obvious to all who inspect the fossil, 

 and compare it with the jaw of a small Didelphys, that contrary to the asser- 

 tion of M. de Blainville, the teeth and their fangs are arranged with as much 

 regularity in one as in the other, and that no argument of the saurian na- 

 ture of the fossil can be founded on this part of its structure. 



" With respect to M. de Blainville's assertion that the jaw is compound, 

 Mr. Owen stated, that the indication of this structure near the lower mar- 

 gin of the jaw of the Thylacotherium is not a true suture, but a vascular 

 groove, similar to that which characterises the lower jaw of Didelphys, opos- 

 sum, and some of the large species of Sorex." 



" Dec. 9, 1838. — A paper on the Phascolotherium, being the second part 

 of the " Description of the remains of marsupial Mammalia, from the 

 Stonesfield slate," by Richard Owen, Esq., F.G.S., was read. 



" Mr. Owen first gave a brief summary of the characters of the Thylaco- 

 therium, described in the first part of the memoir, and which he conceives 

 fully prove the mammiferous nature of that fossil. He stated that the re- 

 mains of the split condyles in the specimen demonstrate their original con- 

 vex form, which is diametrically opposite to that which characterises the 

 same part in all reptiles and all ovipara ; — that the size, figure and position 

 of the coronoid process are such as were never yet witnessed in any except 

 a zoophagous mammal endowed with a temporal muscle sufficiently deve- 

 loped to demand so extensive an attachment for working a powerful carni- 

 vorous jaw; — that the teeth, composed of dense ivory, with crowns covered 

 with a thick coat of enamel, are everywhere distinct from the substance of 

 the jaw, but have two fangs deeply embedded in it;— that these teeth, which 

 belong to the molar series, are of two kinds; the hinder being bristled with 

 five cusps, four of which are placed in pairs transversely across the crown of 

 the teeth, and the anterior or false molars, having a different form, and on- 

 ly two or three cusps — characters never yet found united in the teeth of any 

 other than a zoophagous mammiferous quadruped ; — that the general form 

 of the jaw corresponds with the preceding more essential indications of its 

 mammiferous nature. Fully impressed with the value of these characters, 

 as determining the class to which the fossils belonged, Mr. Owen stated 



