420 Proceedings of the Royal Physical Society. 



to the " placodermic ganoids," and figures a whole series of 

 really undeterminable fragments as bones of the head of this 

 supposed Placoderm, we can hardly follow him. I have 

 carefully gone over all the specimens in the British Museum 

 which he has figured as " upper jaw," " central bone of 

 cranium," etc., and can find no evidence for such determina- 

 tions. I have also examined microscopic sections of Oracan- 

 thus, and find that they consist of selachian dentine ; and we 

 may also appeal to the obvious resemblance which the spines 

 of OracantMis bear to the thin-walled triangular appendages 

 often found associated with Gyracanthus, and which, though 

 not " carpal bones," as Messrs Hancock and Atthey imagined, 

 are unquestionably selachian in their nature. 



The writer of a review of Mr Davis's work, which appeared 

 in the " Geological Magazine " for November 1883, does not 

 believe that the Oracanthi formed the posterior extremity of 

 the body of a Placodermic ganoid, but that " it seems probable 

 that they may have occupied a lateral position on the head 

 of these old Elasmobranch fishes." And if I am right in my 

 generic determination of Oracanthus aryiiigerus, ample corro- 

 boration of this view has now turned up. 



In the Museum of Science and Art, Edinburgh, there is a 

 specimen from the Eskdale beds, showing the head of a small 

 selachian, crushed vertically, along with part of the body, 

 the latter being, however, badly preserved. In the head are 

 broken remains of several large flattened-convex tooth plates, 

 extremely Cochliodont in aspect, but too imperfect for identifi- 

 cation with any known genus or species. But the great point 

 of interest is that each postero-lateral angle of the head pro- 

 jects in a pointed process, like the corner of a Cephalaspis 

 buckler, and that process is — the spine which I have described 

 as Oracanthus armigerus. 



I think there can be no further doubt that the position of 

 the Oracanthus spines is on the head of a selachian, and not 

 on the tail of a Placodermic ganoid. 



Addendum to Cladodus. 



I have long been of opinion that the teeth from Borough 

 Lee, which I described as Clacloclus hicusjndatus, and which 



