Furilter Notes on Carboniferous Selachii. 423 



This statement as to affinities by Mr E. Etheridge, jun., 

 cannot be called in question by any one who has studied the 

 structure of the teeth and jaws of Diodon ; nevertheless, six 

 years afterwards, we find Mr J. W. Davis, at the British 

 Association in 1881, naming this tooth Diodontopsodus, and 

 apparently going back on the idea of its Gymnodont affinities : 

 *' In Diodontopsodus the teeth are extremely like those of the 

 existing fish Diodon " (" Proc. Brit. Assoc, 1881," Trans. Sect., 

 p. 646). And in his large work on the " Carboniferous Lime- 

 stone Fishes " he seems still unable to free himself from this 

 idea. At p. 521 he says — "In searching for the zoological 

 relationship of FiHstodus, a striking and most peculiar resem- 

 blance is at once observed between it and some of the Gym- 

 nodont group of the Plectognath group of fishes at present 

 existing. ... In many respects the fossil teeth from the 

 Mountain Limestone of Yorkshire bear considerable resem- 

 blance to those of Diodon. In the general form of the 

 palatal interior, combined with the semi-circular external, 

 trenchant edge of the tooth, the two are almost identical. 

 ... A comparison of the recent and fossil teeth, however, 

 leads to a natural inference of relationship in some degree, 

 however remote. Evidence is entirely wanting as to the 

 anatomical structure of Pristodus, and I do not wish to lead 

 to the inference that it was more nearly related than is 

 warranted by the peculiar similarity of the teeth." I very 

 much fear, however, that the " peculiar similarity of the 

 teeth " is a very deceptive one after all. 



But although Fristodics cannot have had the remotest 

 affinity with Diodon, it is quite an open question as to 

 whether there may not have been some analogy in the form 

 of the jaws, a couple of these peculiar tooth-plates, one above 

 and one below, forming the whole of the armature of the 

 mouth. Eather against this view, however, is the fact that 

 the height of the crown in these teeth is extremely variable, 

 as may be well seen in the extensive series of P. faleatus in 

 the British Museum, and that in some the apex is more 

 acute, or tending to be mucronate, than in others. 



Mr J. W. Davis's Pristicladodus concinnus seems to me to 



VOL. IX. 2 F 



