260 Messrs. Hancock and Attliey on 



We have shown on a previous occasion that the dental plates 

 of Ctenodus imhricatus are so similar to those of the Australian 

 fish that without other aid thej could not be generically sepa- 

 rated ; and we now see that in the peculiar form and great 

 size of the scales the similarity is equally striking. 



Gyracanthus tuberculatus, Agassiz, and Gladodus mira- 

 hiliSj Agassiz. 



We believe we were the first to point out that certain mi- 

 nute bodies found associated with the remains of these two 

 species are dermal tubercles *. When we wrote our remarks 

 on the subject we described two forms of these peculiar bodies — 

 one considerably larger than the other, and having from four 

 to seven cusps with carinas on their convex surfaces, the 

 smaller form having only two or three smooth points. And 

 we thought both varieties belonged to Gyraccmtlius^ having 

 found the large scattered amidst the small form (which latter 

 was by far the more numerous), and both associated with the 

 spines of that fish and with the teeth of Cladodus. We have 

 long been satisfied, however, that this was a mistake, and 

 that, while the small form is the dermal tubercle of Oyracan- 

 thus, the large variety is that of Cladodus. This is satisfac- 

 torily proved by numerous specimens in our possession, in 

 which the small variety unmixed with the other is associated 

 in large patches with the spines and other remains of Gyra- 

 canthus ; while the large form has occurred on several occa- 

 sions, unaccompanied by the small variety, on the same slab 

 with the teeth of Cladodus and the spines of Ctenacanthus 

 hyhodoides. This has so frequently happened now, that it is 

 impossible any longer to question the fact that the two forms 

 belong respectively to these two large Selachians, And we 

 are also satisfied that the so-called tooth Mitrodus quadri- 

 cornis of Owen is the larger form of these dermal tubercles, 

 as we originally asserted, and consequently belongs to Cladodus 

 or Ctenacanthus J and not to Gyracanthus ^ as we at first 

 thought. 



We have much pleasure in observing that the dermal na- 

 ture of these minute spinous bodies has recently been con- 

 firmed by the researches of Mr. James Thomson, of Glasgow, 

 who has found the large form associated with the teeth of 

 Cladodus mirabilis and the spines of Ctenacanthus hyhodoides'\. 



* See paper entitled " Notes on tlie Remains of some Reptiles and 

 Fishes from the Shales of the Northumberland Coal-field," Ann. Nat. 

 Hist. ser. 4. vol. i. p. 370. 



t See paper entitled " On a Specimen of Acimthodes Wardii from the 



