58 



haz:ir<l a generic or specific name, and I cannot certainly refer it to any of the well- 

 characterised species. 



The subject of fig. Hi, nat. size, 10 a, ruagn. 3 diam., PI. Ill, is a considerable 

 portion of a left mandibular ramus, apparently showing the contour of the lower half of the 

 ascending branch, with a few fractured molars in situ. The symphysial end is broken away. 



Fig. 20, PI. Ill, shows the impression, with two small portions, of the left mandibular 

 ramus. The anterior (ib., a) part of the bone contains the canine, the crown of which is 

 long, strong, subrccurved, and rather obtuse at the apex ; it is supported on a root of twice 

 the length of the crown, which seems to bifurcate at its implanted end. The impression 

 on the matrix shows the fine ridge which was moulded on the usual longitudinal linear 

 groove of the inner side of the ramus. The impressions of the same side of the molar teeth 

 indicate a middle principal pointed conical lobe, and anterior and posterior smaller, but 

 similar lobes. Of these impressions six may be counted, leaving space for premolars 

 between them and the canine. The hind portion of preserved bone is from the lower part 

 of the ascending ramus. 



§ XIV. Genus — Triconodon, Owen, 1800. 1 



In the typo-dentate section of polyprotodont Marsupials a generic form is as well 

 marked in the Purbeck series as is that typified by Phascolotherium in the Lower Oolitic 

 stage. 



But at the Purbeck period the principle of differentiation manifests itself in the present 

 genus by the abrupt assumption of the definite and well-marked triconodont character of 

 the molars (PI. Ill, fig. 7, m l, 2,3) as contrasted with the premolars; and the molars, as 

 defined by shape, are three in number, a reduction rare in the Marsupial order, and 

 unique in association with the four antecedent premolars as, similarly, defined by shape of 

 crown. 



Species 1. — Triconodon mordax, Owen! Plate III, figs. 7, 7 a. 



PI. Ill, fig. 7, represents of the nat. size, and fig. 7 a, magn. 2 diam., the original 

 specimen on which was founded the present genus and species. 



The generic name relates to the form of the crown in the three last teeth (m ], 2, 3), 

 which is subcompressed, antero-posteriorly extended, and divided into three nearly equal 

 cones in the same longitudinal line, the mid cone being very little larger or longer than the 

 front and hind cones ; there is no cingulum on the outer side of the crown, but I may add 



1 Tf/e'is, three ; i<Si os, cone ; obovs, tooth. 

 ' Enc. Brit.,' vol. xvii, 1859, Art. " PalEeontology," p. 161, fig. 86; ' Palaeontology,' 8 vo, 1860, p. 318, 



