Origin of certain Granites, ^c. 59- 



will not now make a similar convenience of hydrotliermalism, but 

 put their shoulders to the wheel, study hard at the collateral sciences, 

 and work out upon a sound basis the true parts which each different 

 agency has played in nature's operations. 



n. — On the Mandible and Mandibulae Teeth of Coohliodonts. 

 By Propessou Owen, F.R.S., F.G.S., Etc. 

 [PLATES III. AND lY.] 



THE extinct cartilaginous fishes represented in ' mountain lime- 

 stone ' and similarly aged carboniferous formations by detached 

 teeth, or dental masses adapted for crushing, have been referred to the 

 Cestraciont family ; and, so far as I know, have now no nearer living 

 representative, in the class of fishes, than the Port Jackson shark 

 {Cestracion PMlippi.) 



The detached condition of the so-called 'palates,' indicates a 

 similar ligamentous attachment of the teeth to a cartilaginous jaw, 

 as in that genus, and the oblique course of their main elevations and 

 furrows (Plate III., Pig. 1, e. g.) is repeated in the arrangement of 

 the series of smaller and more numerous crushing teeth of Cestra- 

 cion ('Palaeontology,' p. 127, Pig 41), so as to have suggested the 

 remark that " it would seem as if the several teeth of each oblique 

 row in Cestracion had been welded into a single dental mass in 

 Cochliodus, the proportions and direction of the rows being closely 

 analogous" {ib. p. 128). 



Whether, however, the resemblance between the carboniferous and 

 existing Australian conchivorous sharks was carried out in the form 

 of the jaws, and especially their forward prolongation with a rasp- 

 like arrangement thereon of pointed teeth for working down to, and 

 extracting from, their sandy beds and burrows, the shell-clad mol- 

 lusks and crustaceans, constituting the food of such fishes, I had 

 not been able satisfactorily to determine at the date of the above- 

 quoted paragraph (8vo. 2nd Ed. 1861). 



I have since, however, been favoured by the Earl of Enniskillen 

 and the Eev. Professor Sedgwick with the opportunity of examining 

 some specimens that settle this point, and indicate that the extinct 

 crushing-sharks of the mountain limestone period, though instruc- 

 tively represented by a lingering member of a once numerous section 

 of Chondropteri, must be relegated to a distinct though conterminous 

 family, for which I propose the name Cocliliodontidce, from what may , 

 be regarded as the representative genus, Cochliodus Ag. (PL III). 



Ihe specimen. Figs. 1 and 2, of the dentary part of the mandible 

 with the teeth of each ramus, though somewhat mutilated as regards 

 both jaw and teeth, shows the confluence of the rami at a symphysis 

 which, in relative position to the teeth, would correspond with the 

 parts of the mandibular rami of Cestracion containing the anterior 

 crushing teeth. The fore-part of the symphysis itself is, indeed, 

 broken away ; but its small vertical depth at the point of fracture, 

 together with the small tranverse extent, and the angle at which the 

 rami converge thereto, afford no ground for assuming that the- 



