414 E. S. GOODEIOH. 



broken premolars.^ In front of these Owen detected the 

 sockets for six teeth. 



Osborn has lately (15) discovered a young molar emerging 

 from the jaw just behind and within the posterior molar. 



The British Museum specimen (PI. 26, fig. 4) is a 

 portion of the right ramus, inner view. 



This fossil has been partially figured by Osborn in his first 

 treatise (14), who took it to belong to a left ramus; but in 

 his later paper (15) he recognised its true character by the 

 presence of the '^ double internal cusps [of the molars], by the 

 cingulum upon the premolar, and by the faint mylohyoid 

 groove near the lower border/' adding in a note that "it 

 would be well to run the risk of injuring one of these molars 

 to expose the external cone." 



The jaw, which is figured here complete and in detail for the 

 first time, although much broken is really the most instructive 

 of the four specimens extant of this genus, as regards the 

 structure of the molars. In front are the traces of four teeth, 

 followed by an entire premolar. The latter possesses a late- 

 rally compressed crown bearing one large cusp, a very small 

 anterior cingulum cusp, and a posterior heel. On the whole 

 this tooth is very similar to the premolars of the other Amphi- 

 therium jaws. The molars, of which there are five remaining, 

 when I first examined them displayed only the two nearly 

 equal and pointed cusps of the inner margin, and a simple low 

 posterior heel (as shown in the figure by the third and fourth 

 molars) ; by carefully clearing ofi" the matrix I have exposed 

 the large external cusp (protocone) in the first, second, and 

 fifth molars (see woodcuts, figs. 1 and 2). In the latter tooth 

 I have also exposed the full extent of the posterior heel, 

 which is seen to rise on the external margin into a pronounced 

 cusp ; the internal cusp is hardly distinguishable from the 

 general margin of the heel at its postero-internal angle. The 

 heel is somewhat narrower than the body of the tooth at the 



^ The posterior premolar bears a small internal cusp (= the deuteroeone 

 of Scott P). 



