Dr. R. H. Traquair—Carboniferous Selachii. 81 
VII.—Norers on Carsonirerous Sexnacutt.! 
By Dr. R. H. Traquair, F.R.S., F.G.S. 
The Cladodontide. 
HE teeth known as Cladodus (type ©. mirabilis, Ag.) have a 
flattened, transversely elongated, sub-elliptical or reniform base, 
the anterior margin being straighter than the posterior and often 
shghtly excavated in the middle. Anteriorly the base is thick, and 
generally shows a groove separating the truly basal from the coronal 
portion, while the posterior margin is thin owing to the downward 
and backward slope of the upper surface. From this upper surface 
anteriorly spring a number of cones or denticles, of which the median 
is the longest; it is flanked by lateral denticles, of which an outer 
one on each side is longer than those intermediate. The larger 
denticles, at least, are flattened antero-posteriorly and have lateral 
cutting margins. 
There are two exceedingly well-marked species of common 
occurrence in the British and Ivish Carboniferous Limestone, namely, 
C. mirabilis, Ag., and C. striatus, Ag. C. marginatus, Ag., I also 
believe to be a good species, as well as C. Milleri, Ag. On C. acutus, 
Ag., conicus, Ag., basalis, Ag., Hibberti, Ag., and parvus, Ag., I offer 
no opinion, not having seen the types ; but as to the new species added 
by Mr. J. W. Davis in his large work on the fossil fishes of the 
Carboniferous Limestone series of Great Britain” there is scarcely 
one which will stand the test of careful comparison with the common 
species described by Agassiz. C. Hornet, Dav., C. elongatus, Dav., 
and C. curtus, Dav., are in my opinion simply synonyms of C. striatus, 
Ag.,— C. mucronatus, Dav., and destructor, Davis, of C. mirabilis, Ag. 
It is rather difficult to give any opinion upon C. curvus, Davis. 
In the Edinburgh Museum, and in the Collection of the Geological 
Survey of Scotland, there are a few teeth of what is evidently a new 
species of Cladodus, from the Lower Carboniferous rocks of Eskdale 
in Dumfriesshire, though I refrain on the present occasion from giving 
ita name. In these teeth the surface of the cones is perfectly smooth 
and glossy, and in the absence of striations they approach C. van 
Hornet and prenuntius of St. John and Worthen. The thought has 
struck me, is it possible that this undoubted Cladodus may repre- 
sent the dentition of Ctenacanthus costellatus, the unique specimen 
of which, with the spines in situ, occurred in the same beds? It will 
be recollected that the only tooth visible in the specimen of Ctena- 
canthus costellatus was an imperfect one, but its one visible cusp was 
smooth. If there is any connection here, the specimen of Ct. costel- 
latus must have been a young individual, as these teeth indicate a 
fish of much larger size. 
This brings up once more tbe question of the correlation of 
Cladodus and Ctenacanthus, a question which I must admit is still 
involved in great obscurity. When I wrote my description of 
Read before the Royal Physical Society of Edinburgh, 18th January, 1888. 
2 Trans. Roy. Dub. Soc. 1883. 
DECADE III.—VOL. V.—NO. II. 6 
