422 Proceedings of the Royal Physical Society. 



genus. Other Gyracanthi, etc., are found in every stage of 

 " polishing off." But this phenomenon is by no means pecu- 

 liar to the spines and other iish remains from Loanhead ; it 

 is tolerably frequent elsewhere, and is apt to lead into error 

 those who have not yet learned to take it into account, 

 Pleuracanthus erectus, Davis (Quart. Joiirn. Geol. Soc., vol. 

 XXX vi., p. 326), is to my mind nothing but an eroded speci- 

 men of PL Icevissimus, Ag., the " very blunt-pointed " char- 

 acter of the denticles being thus amply accounted for ; and 

 I have a specimen of PL elegans, Traq., from Loanhead, which 

 shows precisely the same condition. PL Wardi, Davis {ih., 

 p. 334), probably owes the bluntness of its denticles to the 

 same cause. And I feel pretty well persuaded that T. Stock's 

 Lophacanthus Taylori {Ann. and Mag, Nat. Hist., 5th ser., 

 vol. v., p. 217) is nothing but a worn specimen of Pleuracan- 

 thus {Orthacanthus) cylindricus, Ag. 



Peistodus falcatus, Davis {ex Agassiz MS.). 



Mr Davis, in his large work on the Carboniferous Lime- 

 stone Fishes of Great Britain, in describing the remarkable 

 tooth, to which Agassiz had given the name Pristodus fal- 

 catus, makes no reference whatever to the fact that a closely 

 allied species had been already, in 1875, figured and described 

 by Mr E. Etheridge, jun., in the *' Geological Magazine," 

 under the name of Petalorhynchus (.-) Benniei.'^ 



Mr E. Etheridge also mentions that he had been informed 

 by Mr W. Davies^ that Mr W. Home had exhibited a similar 

 tooth from Wensleydale, at the Bradford meeting of the 

 British Association in 1873, and goes on to say — " Mr Davies 

 is also much impressed with its resemblance externally to 

 the uncovered teeth of the Parrot fishes generally, but more 

 especially to the Diodons ; but as the fish which bore this 

 tooth was undoubtedly a Selachian, and the structure of the 

 tooth, within the mouth, so different to that of the Diodons, 

 it can have no affinity with these recent fishes, although very 

 sujraestive of a Selachian with a similar form of mouth." 



•co^ 



1 Geol. Mag., Dec. 2, vol. ii., p. 242, pi. viii., figs. 3 and 4. 



2 Formerlv of the British Museum. 



