2G0 



Downs, which was purchased of the collector by Mr. Benjamin Boyd, and subse- 

 quently, with the rest of Mr. Boyd's collection, acquired by the British Museum, is 

 from the same formation and locality as the skull above described, which fell into 

 Mr. Isaac's hands. 



This mandible agrees so closely, not only in the shape, structure, and other characters 

 of the teeth, saving the difference of upper and lower, but also in the dimensions of these 

 and of the proportion of the jaw-bone preserved, that it might well have been part of the 

 same individual ; it certainly belongs to the same species. 



Comparing the type specimen of Nototlierium Mitclielli, Ow.*, with the answerable 

 part of the above-mentioned mandible, the correspondence in size and configuration 

 is such as to support the reference of the present more complete specimen to that 

 species. 



The depth of the mandible behind the last molar is 3 inches 9 lines in the first 

 described, it is 3 inches 8 lines in the present specimen ; the thickness of the mandible 

 below the last molar is 2 inches 6 lines in both specimens. The antero-posterior extent 

 of the two last molars in the original fragment with mutilated crowns is 3 inches 4 lines ; 

 in the more perfect mandible (Plate XXXVIII. figs. 1 & 2 ; Plate XLIV. figs. 1 & 2, 

 m 2, m 3) it is 3 inches 6 lines ; from the back of the last molar to the entry of the dental 

 canal (Plate XXXVIII. fig. 2, 0) is 2 inches 9 lines in both specimens. The place and 

 degree of inflection of the under margin and angle of the jaw (ib. a & d) are the same 

 in both. 



Referring on these grounds the mandible (Plate XXXVIII. figs. 1 & 2) to Nototherium 

 Mitclielli, the cranium and upper jaw answering to that lower jaw must be referred to 

 that species. 



The mandible in question consists of the two rami mutilated at both ends, but fortu- 

 nately retaining their natural confluence at the symphysis, of which a longitudinal extent 

 of 3 inches 8 lines is preserved (ib. figs. 2, 3, s) ; this gives the angle of divergence of 

 the horizontal rami from the place of confluence (ib. id.). It shows that the interval 

 between the right and left mandibular condyles agreed with that between the articular 

 cavities in the skull (Plate XXXVII. fig. 3, g, (j) ; and that the distance of the condyle 

 from the fore part of the first molar (d 3) was the same as that, viz. 12 inches, from the 

 fore part of the first molar to the joint for the condyle in the upper jaw. 



So much of the ascending ramus as is preserved, which closely corresponds with that 

 in the type jaw, shows the same oblique direction of the curve (Plate XXXVIII. fig. 1, 

 a, b, d) by which the lower border graduates into the hind one of the rising branch : 

 the curve changes slightly on rising to the level of the alveoli, being then feebly con- 

 cave above the anterior inflected part of the lower margin ; it becomes convex where the 

 border is again inflected, and above this the hind border of the ascending ramus, after con- 

 tracting, expands transversely, apparently to support the condyle. The angle or anterior 



* " Report on the Extinct Mammals of Australia, ifec," in Report of the British Association &c. for 1864, 

 p. 13, pi. 4 ; and Cut, fig. 1, p. 42 (sujord). 



