From the Carboniferous of Eskdale. 7 



ever, as regards Ctenacanthus, there has been a good deal of specula- 

 tion. Agassiz was inclined to refer Psammodiis to Ctenacanthus ;^ 

 hut as Sir Philip Egerton rightly remarked, "The occurrence, how- 

 ever, of the latter genus of Ichthyodorulites in the Coal-measures 

 tmassociated with teeth of the genus Psammodus would militate 

 against this suggestion." " Founding upon the occurrence together 

 of spines of Ctenacanthus (Ct. furcicarinatus, N.) with a species of 

 Orodus (0. variahilis, N.) in the Waverley shale at Vanceburg, 

 Kentucky, Prof. Newberry has j^ut forward the view that Orodus 

 formed the dentition of the fishes bearing the genus of spines with 

 which we are concerned.^ But the view which has found most 

 favour is that which has been advocated by the late Messrs. Hancock 

 and Atthey of Newcastle,* and by Mr. James Thomson of Glasgow,^ 

 namely, that the dentition of Ctenacanthus is to be sought in the teeth 

 so well known as Cladodus. Certainly, even without evidence of 

 association, the identity of these genera is indeed suggested by the 

 obvious general resemblance which the Ctenacanthus spine and the 

 Cladodus tooth bear to the certainly correlated spines and teeth 

 of the Mesozoic Hybodus. Komanowski has indeed described a 

 very hybodont-Iooking spine as Cladodus tenidstriatus, from its 

 association with teeth referable to that genus,^ and Mr. J. W. Barkas 

 has gone even so far as to propose the abolition of the terms Cladodus 

 and Ctenacanthus altogether, and to merge their species in the one 

 genus Hybodus.'^ It is at all events satisfactory to find that the 

 dentition of the present species was Cladodont in character, and 

 that we have in this a corroboration of the wide-spread idea that 

 the characteristic teeth and spines of the Carboniferous era, known 

 respectively as Cladodus and Ctenacanthus, and represented by so 

 many species, were borne by the same genus of fishes. 



Founded also upon analogy with the extinct Hybodus and the 

 recent Cestracion and Acanthias, a very genei'al opinion has been 

 entertained that Ctenacanthus must, like those genera, have possessed 

 two dorsal fins with a spine in front of each. This question is 

 settled by the present specimen, which shows the two dorsal spines 

 in situ, the spines closely resembling each other, though the anterior 

 one is slightly the longer, and the posterior somewhat more straight 

 in contour. 



Although at least one genus of Palgeozoic sharks, Gyracanthus, 

 must have been provided with pectoral, or in any case paired, spines, 

 the paired fins are, in this case, clearly destitute of any such 

 appendages. And no Ctenacanthoid or Hybodoid spine has ever 

 been shown to possess that peculiar want of bilateral symmetry 

 which points out those of Oyracanthus as non-median. 



Prof. Hasse has indicated his belief that, in the Palseozoic Selachii, 



1 Poissons Fossiles, vol. iii. p. 171. 



2 Quart. Journ. Geol. Soc. 1853, p. 282. 

 ^ Pal. Ohio, vol. ii. p. 54. 



* Ann. and Mag. Nat. Hist. (4) ix., 1872, p. 260. 



5 Trans. Geol. Soc. Glasgow, vol. iv. (1861), p. 59-62. 



^ Bull. Soc. Nat. Moscow, vol. xxxvii. (1864), pp. 157-170. 



'' Proc. Eoy. Soc. New South Wales, 3 Oct. 1881. 



