Zoological Society. 483 



the family, and together with the trenchant character of the premolars 

 in the Meminna and Hyeomoschus, seems to associate with them the 

 genera Dichobune, Bichodon, and Cainotherium^ . 



This characteristic form of the penultimate upper milk tooth, 

 namely the want of the inner crescent of the anterior pair, with the 

 presence of the additional cusp in front, plainly marks as this tooth, 

 that which Prof. Owen has indicated as the penultimate premolar in 

 his recently discovered genus Hyopotamus, and as the last premolar 

 in his also newly-described genus Bichodon ; the tooth behind it in 

 each case being the last milk tooth, which always agrees exactly with 

 the true molars, but is distinguishable from them by its suddenly 

 diminished size. The series of upper molars of the latter animal 

 have been placed, in the published figure, to the extent of one tooth 

 too far back ; were they brought forward to their true position, the 

 tripartite tooth below, which, according to all laws of form and suc- 

 cession, can be no other than the last milk molar, (of which the suc- 

 cessor has not begun to appear,) w^ould antagonize by its anterior 

 pair of crescents with the space in front of the posterior pair in the 

 penultimate milk tooth above. Of the Hyopotamus Vectianus, the 

 figure represents a series of the crowns of five upper molars, of which 

 the first is, as I have before observed, manifestly a penultimate milk 

 tooth. These being represented without any appended portion of 

 jaw, and no mention being made in the text as to whether they were 

 found connected, it seems rather probable that such was not the case, 

 and in the side \iew roots are added in outline to certain of the teeth 

 and not to others, which makes that matter still more doubtful. At 

 all events, this condition of things could not possibly have co-existed 

 with that represented in the lower jaw attributed to the same species ; 

 since in the upper series of teeth we may count ten principal trans- 

 verse eminences, while in the lower series of five molars, which ought 

 to fit them, there are only eight depressions : besides which, it is im- 

 possible that the elevated summits presented by the trenchant lower 

 premolars, with the correspondingly deep notch which their interval 

 affords, could ever fit the comparatively diminutive elevations and 

 depressions presented by the foremost teeth above. The lower true 

 molars, however, show a much more worn condition than the upper 

 ones ; but even if it should be possible that the series of upper molars 

 represented were in place and in use at the same time, it is evident 

 that the foremost of them cannot be premolars f. 



* In the true Moschus the premolars have much the same form as in the gene- 

 rality of Ruminants ; the incisors are uniform and nearly equal in size, and the au- 

 ditory bulla is small : in the Meminna, and in those to which the generic name 

 Trayulus has been applied (which I can see no reason for separating from it), the 

 last upper premolar alone is bicuspid, the other two and all the lower ones being 

 trenchant ; the two median incisors are expanded, the others narrowed and curved 

 outwards to make room for them, and the auditory bulla swollen : Hyeomoschua 

 only differs from these in the penultimate upper premolar, wiikh though trenchant 

 is short, and when worn down has the appearance of being simply conical. 



t I do not claim to be the sole discoverer of these incongruities (apparently 

 the results of a too hasty determination), since I am aware that the true nature 

 of the tripartite inferior tooth in the Dichodon has been perceived by some emi- 

 nent comparative anatomists and naturalists ; but I am here compelled to attempt 



32* 



