60 REPORT — 1842. 



I shall subsequently describe. What M. de Blainville has mistaken for an 

 articular fissure, " une sorte d'6chancrure, articulaire un peu comnae dans 

 les poissons," must be the entering angle or notch, either above or below the 

 true articular condyle. 



The angle of the jaw in the original fossil is produced backwards in the 

 form of a process, as in the insectivorous and in all the carnivorous Mam- 

 malia, with the exception of the seals ; but it could not be determined in 

 that specimen whether this process was likewise bent inwards in the way 

 which so strikingly characterizes the Marsupialia. A very complete half- 

 lower jaw from Stonesfield, obtained since my paper was printed in the 

 Geological Transactions, determines this question in the negative ; and at the 

 same time, therefore, turns the scale of evidence in favour of the affinities 

 of the present ancient mammal to the placental insectivora. 



Before, however, describing this fossil, I shall proceed to offer a few ob- 

 servations on the second specimen of Amphitherium figured in my paper in 

 the Geological Transactions ; and on the evidence which it affords of the 

 affinities of this most interesting genus. 



In this specimen the whole of the exposed surface of the lower jaw, with 

 the exception of the coronoid, articular and angular processes, is entire ; the 

 smooth surface near the anterior extremity of the jaw is in bold relief, and 

 slopes away at nearly a right angle from the rougher articular surface of the 

 elongated symphysis. It may be supposed that this symphysial surface, 

 which at once determines the side of the jaw, might be obscured in the 

 plaster cast studied by M. de Blainville, but there is no possibility of mis- 

 taking it in the fossil itself; it is long and narrow, and is continued forwards 

 in the same line with the gently convex inferior margin of the jaw, which 

 thus tapers gradually to a pointed anterior extremity, precisely as in the jaws 

 of the Didelphys as well as in other Insectivora, both of the marsupial 

 and placental series. Its lower margin presents a small but pretty deep 

 notch, which possesses every appearance of a natural structure, and a corre- 

 sponding but shallower notch is present in the same part of the jaw of the 

 Myrmecobius. In the relative length of the symphysis, as in its form and po- 

 sition, the jaw of the Amphitherium corresponds with that of the Didelphys, 

 Myrmecobius and Gymnurus. A greater proportion of the convex articular 

 condyle is preserved in this than in the foregoing specimen, and it projects 

 backward to a greater extent. The precise contour of the coronoid process 

 is not so neatly defined in this as in the first specimen of Amphitherium, but 

 sufficient remains to show that it had the same height and width. 



The exposed surface of the coronoid process is slightly convex. The sur- 

 face of the ascending ramus of the jaw is entire above the angle, whence we 

 may conclude that if the process from the latter part had been continued 

 directly backwards, it would also have been entire ; but the extremity of the 

 angular process is broken off, proving it to have originally inclined inwards 

 or towards the observer : as, however, the greater part of the angle is entire, 

 it could not have been inflected to the same extent as in the Didelphys, 

 Dasyurus, or the Phascolotherium next to be described. A groove is ex- 

 tended from the lower end of the articular condyle forward to the orifice of 

 the canal for the dental artery, where it divides ; the upper branch terminates 

 in the dental orifice, the lower and larger division is continued forward near 

 the lower margin of the jaw, and is gradually filled up half way towards the 

 symphysis : this smooth vascular groove has no resemblance to an articular 

 fissure. There is a broader and snorter groove in the corresponding part of 

 the jaw of the Myrmecobius ; and a narrower groove in that of the Wombat. 

 The alveolar wall of the posterior grinders makes a convex projection, cha- 



