276 Mr. A. S. Woodward on the Myriacantliidge. 



Af7/riacantJms *, It is a fossil evidently havin,s^ a wide range 

 in Jurassic rocks, for, besides the English Liassic species, 

 others are known from the Upper Jurassic of Bavaria t ; and 

 it is thus remarkable that, until the present time, the precise 

 rekitionships of the " genus " should have remained altogether 

 undetermined. The British Museum now furnishes materials 

 for the solution of the interesting problem ; and it is the 

 object of the present paper briefly to record the facts already 

 available, with the zoological inferences that seem deducible 

 therefrom. 



Myriacanthus is a long slender spine, somewhat laterally 

 compressed, with a hollow internal cavity opening at the 

 base. There is no indication of an inserted portion in the 

 known specimens, the lateral ornament of small tubercles 

 extending over the whole of the sides, except quite at the 

 distal extremity ; a sparse irregular series of large, thorn- 

 shaped, spinous tubercles is arranged along each edge of tlie 

 somewhat flattened, smooth posterior face, while a few similar 

 tubercles also occasionally occupy the median line of this face ; 

 and the anterior edge of the spine is provided with one such 

 series of spinelets, at least in part of its extent. 



The first clue to the true nature of this Ichthyodorulite 

 was received by the British Museum in 1870, when tlie fine 

 Liassic fossil described by Egerton as Ischyodiis ortJiorhinus \ 

 was added to the collection. In Egerton's memoir, however, 

 there is no allusion to the fact, which seems to have also 

 escaped subsequent observers ; and the only pala3ontologist 

 who has recognized a striking novelty in the fossil is Prof. 

 Dr. K. A. von Zittel §, who proposes to assign to it the 

 generic name of Metopacanthus. 



The so-called " Ischyodus orthorhinus^^'' as made known by 

 the type specimen, is remarkable in many respects. Although 

 dating back to so remote a period as that of the Lias, it 

 exhibits a singular prolongation of the snout precisely similar 

 to that of the existing Callorhynchus. In the enormous size 

 of the median frontal spine, however, it still remains unique. 

 The last-named appendage is nearly similar in form to that 

 of Squaloraja \\ ; when not abraded its surface is covered 



* L. Agassiz, Kech. Poiss. Foss. vol. i. (18S7), p. 37. 



t MyriacanUiUS fra7ico7nc2ts, G. v. Miinster, Beitr. Petrefakt. pt. iii. 

 (1840), p. 127, pi. ill. ficr. 8. 



X Sir P. Egerton, " On a new Chimseroid Fish from the Lias of Lyme 

 Kegis," Quart. Journ. Geol. Soc. vol. xxvii. (1871), pp. 275-278, pi. xiii. 



§ K. A. von Zittel, ' Handbuch der Palaeontologie,' vol. iii. (1887), 

 p. 110. 



II W. Davies, " On the Rostral Prolongation of Squaloraja poly- 

 spondyla, Ag./' Geol. Mag. vol. ix. (1872), pi. iv. figs. 1-3, 5. 



