298 ON FOSSIL FISH-TEETH. 



tliffered'also in another, and very marked, respect. The flatter teeth in 

 all our specimens had five horns, that is, the two terminal points, and 

 tliree intermediate; the more elevated teeth on the contrary had only four 

 horns, that is, the two terminal points and two intermediate horns. 



This fact at once suggested that these two kinds or varieties might 

 fit into each other ; and on examining further it was found that in 

 several cases these flatter teeth fitted perfectly to the other and more 

 elevated teeth. There remained, therefore, no doubt, that whatever 

 their position in the jaw might be, we had in these two groups the upper 

 and the lower-jaw teeth of similar individuals. 



There was, however, no direct evidence as to which belonged to the 

 upper jaw, and which to the lower. In almost all cases the' tooth-mass 

 ■was detached from the bone which originally supported it. One speci- 

 men still retained a portion of the bone, and with considerable care 

 I was able to relieve this from the ferruginous clayey concretion which 

 had formed round it, and to discover in part the true form of the bone. 

 This is seen Fig. 1. PI. xiv. 



It also appeared that the bony or lower layer of the teeth was in all 

 cases deeper and stronger and thicker, in the more elevated and more 

 prominently ridged teeth, than in the flatter specimens. From this I 

 was led to conclude, that the teeth having the more massive and strong- 

 er osseous attachment belonged to the upper jaw, while the flatter teeth 

 probably belonged to the lower jaw. If this be granted, out of the 

 seventeen teeth which I received from Mr. Hislop nine were upper- 

 jaw teeth of Ceratodus, of different kinds, and eight belonged to the 

 lower-jaw. 



Agassiz noticed the curious fact, that out of seventeen specimens 

 to which he had access, no less than eleven had their hornlike projec- 

 tions on one side, or belonged to the same side of the mouth ; and only 

 six to the opposite. In the same way it is curious that out of the nine 

 upper-jaw specimens which we have, six belong to the same side of the 



