OWEN NOTOTHERIUM. 183 



border to a breadth of 1 inch. 6 lines, and then begins to expand as 

 it advances ; this is a very significant evidence of the relationship of 

 Nototherium MitchelU with the cranium of Zygomaturus. The sides 

 of the upper symphysial channel, in advance of the first molar, ter- 

 minate above in a ridge, which is concave outwards, through the 

 lateral contraction in front of the molar series. The anterior outlet 

 of the dental canal is situated 1 inch 3 lines below this ridge, opposite 

 the fore part of the socket of the first molar. 



The right and left molar series converge a little anteriorly, with 

 a slight concavity towards each other. From the outside of the socket 

 of the right to that of the left last molar is 5 inches 6 lines ; the 

 extreme breadth of the lower jaw at the same part is 7 inches 9 

 Hnes, which is due to the great outswelling of the rami at that part. 

 At the under and back part of the symphysis there is a semicircular 

 depression, 1 inch 8 lines, across, bounded anteriorly by a sharp 

 wall, concave backwards. 



Such are the chief additional facts relative to the structure o± the 

 lower jaw and teeth of the Nototherium MitchelU, which are derivable 

 from the more perfect specimen in the British Museum, as compared 

 with the original, in the College of Surgeons, on which the species 

 was founded. There remains to be determined the degree of corre- 

 spondence between this lower jaw with its dentition, and the cranium 

 and teeth of the bilophodont marsupial to which the name Zygoma- 

 turus has been applied. 



The photographic figures, and the subsequently received cast of 

 that cranium, showed a well-marked difference from Diprotodon in 

 the much greater extent of the anterior origin, or base of attachment 

 of the zygomatic arch in. the smaller bilophodont marsupial : and 

 this character has served to determine the nature of a portion of the 

 right side of the upper jaw, with three molar teeth, and an almost 

 coextensive anterior base of the zygomatic arch (Plate IX. fig. 5) of 

 a similar-sized bilophodont forming part of the collection of Austra- 

 lian fossils ia the British Museum. The difference between this and 

 Diprotodon is most conveniently exemplified by an almost similar 

 fragment of the right upper jaw, with the anterior base of zygomatic 

 arch (z) and a single molar (m-z), with part of the sockets of the 

 preceding and succeeding tooth (/6. fig. 6), in the collection of fossils 

 sent by the I^atural History Society' at Worcester. The difference 

 above pointed out in the surface of the enamel of the lower molar 

 teeth of Nototherium and Diprotodon, is here as strikingly exempli- 

 fied in the enamel of the upper molars. The ridges, instead of being 

 directly transverse as in Diprotodon, show the same slight degree of 

 obhquity as in the lower molars of Nototherium. The summits of 

 the ridges show a slight concavity directed backwards, due in part to 

 the production of the inner and back part of each ridge, — a modifi- 

 cation which, from the analogy of Macropus, might have been 

 anticipated in the upper molars of Nototherium. 



The fore and aft extent of the thi-ee molars in the present frag- 

 ment of upper. jaw corresponds with that of the three middle molars 

 of the lower jaw of Not. MitchelU ; their transverse breadth is greater 



