346 FOSSILS FROM THE 



have found occumng in considerable numbers in a shelly de- 

 j)osit of the island of Eigg; and are of great interest and 

 beauty. They are formed of true bone, and thi-ckly sprinkled 

 over, towards their bases, with the characteristic life-points ; 

 whereas towards the apex they abound in anastomising canals, 

 which throw out to the sides and points of each tooth nume- 

 rous minute, nearly parallel branches, that give to the bone 

 in these parts a structure very much approximating to ivory. 

 It would seem as if in these ancient teeth we had caught bone 

 passing into that finer substance of which the teeth of all 

 the higher vertebrata, and all the reptile teeth of all the sau- 

 roid fishes of the Coal Measures, are composed. 



My earlier found specimens of Coccosteus, which indicated 

 this marked peculiarity in the setting of the teeth, were in 

 so imperfect a state of keeping, that I could not demonstrate 

 its existence. I may, however, be permitted to state to the 

 Association the line of inference on which I deemed myself 

 justified in soliciting inquiry regarding it ; and my first, and, 

 for about nine years, only reference to it, amounted to no 

 more. In three specimens of jaws, unlucky fractures sepa- 

 rated the anterior portion, containing the teeth in the sym- 

 physis, from the middle portion, containing the teeth of the 

 molar region ; and though all three presented the peculiarity 

 of position which seems to render it impossible that the two 

 groupes could have acted in the same plane, or with the same 

 action of the condyles, it was of course possible that the pe- 

 culiarity was an effect of misplacement. The chances, how- 

 ever, against the occurrence of exactly the same misplacement 

 in three jaws seemed very considerable; — each of the ante- 

 rior pieces of jaw separated by the fracture had four sides, only 

 one of which was furnished with teeth. It was as one chance 

 out of four, then, that these teeth should be presented in one 

 of the jaws (supposing the misplacement of the fractured piece) 

 in the line of the symphysis ; — it was as one chance out of 



