102 Dr. R. H. Traquair—Carboniferous Selachir. 
Mr. W. Davies’ that Mr. W. Horne had exhibited a similar tooth 
from Wensleydale at the Bradford meeting of the British Associa- 
tion in 1878, and goes on to say :—‘‘ Mr. Davies is also much im- 
pressed 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 suggestive of a Selachian with a similar form of 
mouth.” This statement as to affinities by Mr. R. 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 
to 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 Limestone Fishes he seems still unable to free 
himself from this idea. At p. 521 he says:—‘“‘In searching for the 
zoological relationship of Pristodus, a striking and most peculiar 
resemblance is at once observed between it and some of the Gymno- 
dont group of the Plectognath group of fishes at present existing. 
. . - In many respects the fossil teeth from the Mountain Limestone 
of Yorkshire bear considerable resemblance 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. Hvidence 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 Pristodus 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. Rather 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. falcatus 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 be 
nothing more or less than a crushed specimen of a species of 
Pristodus with a more than usually mucronate apex. 
1 Formerly of the British Museum. 
2 My friend Mr. A. Smith Woodward writes to me that he has, from an examina- 
tion of specimens from Derbyshire, come to the conclusion that Pristodus Benniei (R. 
Eth., jun.) is after all distinct specifically from P. faleatus, Ag. Concinnus (Davis) 
he also is inclined to regard as distinct, and in that case all three names will stand as. 
species of Pristodus. 
