Geological Society. l^^ 



fossils, has since been regarded as one of the proofs of their Saurian 

 nature ; but the exceptions 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 MammaUa, are well established, and have 

 been long known. The insectivorous Chrysochlore, in the order 

 Ferae, has eight molars in each ramus of the lower jaw ; the insec- 

 tivorous 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 formulae of the carnivorous Cetacea, again, de- 

 monstrate the fallacy of the argument against the mammiferous cha- 

 racter of the Thylacotherium founded upon the number of its molar 

 teeth. From the occurrence of the above exceptions in recent pla- 

 cental Mammalia, the example of a like 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 mar- 

 supials, and such an addition to our zoological catalogues has, in 

 fact, been recently made. In the Austrahan quadruped described 

 by Mr. Waterhouse under the name of Myrmecobius* an approxima- 

 tion 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 insjiect the fossil and 

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

 assertion of M. de Blainville, the teeth and their fangs are arranged 

 with as much regularity in the one as in the other, and that no ar- 

 gument of the Saurian nature of the fossil can be founded on this 

 part of its structure. 



With respect to M. de Blainville's assertion that the jaw is com- 

 pound, Mr. Owen stated, that the indication of this structure near 

 the lower margin of the jaw of the Thylacotherium is not a true 

 suture, but a vascular groove similar to that which characterizes 

 the lower jaw of Didelphys, Opossum, and some of the large species 

 of Sorex. 



In a memoir to be brought forward on another occasion, Mr. 

 Owen intends to describe the other genus found at Stonesfield, and 

 for which, on account of its marsupial affinities, he proposes the name 

 of Phascolotherium.-f 



A notice by R. W. Fox, Esq., was afterwards read, " On the 

 Formation of Metallic Veins by Voltaic Agency." J 



In this communication Mr. Fox says, that he has succeeded not 

 only in forming well-defined metalliferous veins in a crack in the 

 middle of masses of clay by means of voltaic agency, but also in im- 

 parting to the clay a laminated or schistose structure ; the veins and 

 lamiQse being perpendicular to the voltaic forces. In some instances 



[• See Lond. & Edinb. Phil. Mag. vol. ix. p. 520; vol.xi.p. 200.— Edit.J 

 [f A list of the fossils associated witli tlicse marsupial remains in the 



Stonesfield slate, drawn up by Mr. De la Ikclie, will be found in Phil. Mag. 



and Annals, N. S. vol. vii. ji. 2)7. — Edit.] 



[I See Lond. and Edinb. Pliil. Mag. vol. xi. p. 203. — Edit.] 



Phil. Mag. S. 3. Vol. 14. No. SC. Feb. 1839. L 



