Dr. Rk. H. Traquair—Carboniferous Selachit. 101 
Iil.—Furruer Nores on Carsonirerovus SEeLacuit.! 
By Dr. R. H. Traevair, F.R.S., F.G.S. 
Anodontacanthus and Pleuracanthus. 
die 1881? Mr. J. W. Davis proposed the genus Anodontacanthus 
for certain straight spines resembling Plewracanthus, but 
differing in the absence of the two rows of denticles. Three species 
are included:—A. acutus and obtusus, from the Coal-measures of 
Yorkshire, and A. fastigiatus, from the Blackband Ironstone of 
Carboniferous Limestone age at Loanhead, near Edinburgh. 
Toffer no criticism on the two Yorkshire species, nor have I seen the 
type of the Midlothian 4. fastigiatus. In the large collection of spines 
which I have from Loanhead, there are, however, many which I refer 
without doubt to the last-named species. Now, although some of these 
are smocth and without denticles, others show, in all stages of apparent 
wearing away, undoubted stumps of denticles, whereby the species 
fastigiatus falls into Pleuracanthus, as that genus at present stands. 
It is to be noted that a large number of the spines found in this 
Ironstone (Loanhead and Borough Lee, No. 2) are singularly worn 
or eroded all over, as if they had been long exposed to the action of 
agencies, chemical or mechanical, tending to destroy the surface. I 
have seen a spine of Gyracanthus from that bed having every vestige 
of the surface ornament, so elaborate in that genus, removed, and I 
had to examine it microscopically before I felt absolutely sure of its 
genus. Other Gyracanthi, etc., are found in every stage of “ polishing 
off.” But this phenomenon is by no means peculiar to the spines 
and other fish 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 
(Q.J.G.S. vol. xxxvi. p. 826), is to my mind nothing but an eroded 
specimen of Pl. levissimus, Ag., the ‘‘ very blunt-pointed ” character 
of the denticles being thus amply accounted for, and I have a speci- 
men of Pl. elegans, Traq., from Loanhead, which shows precisely the 
same condition. Pl. Wardi, Davis (ib. p. 834), probably owes the 
bluntness of its denticles to the same cause. And | 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 Pleuracanthus (Orthacanthus) cylindricus, Ag. 
Pristodus falcatus, Davis (ex Agassiz MS8.). 
Mr. Davis, in his large work on the Carboniferous Limestone 
Fishes of Great Britain, in describing a remarkable tooth to which 
Agassiz had given the MS. name Pristodus falcaitus, makes no 
reference to the fact that a closely allied species had been already, 
in 1875, figured and described by Mr. R. Etheridge, jun., in the 
GuroLocicaL Macazrnz, under the name of Petalorhynchus? Benniei.? 
Mr. R. Etheridge also mentions that he had been informed by 
1 Read before the Royal Physical Society of Edinburgh, February 15th, 1888. 
2 Q.J.G.S. vol. xxxvii. p. 427. 
3 Gzou. Mac. Dec. II. Vol. II. p. 242, Pl. VIII. Figs. 3 and 4. 
