Mr. A. S. Woodward on the Myriacantliida3. 279 



present writer to justify the assertion of the generic identity 

 of these two fishes. 



The so-called Iscliyodus (or Metopacanthus) orthorJiiniis 

 thus possesses (i.) a dorsal fiu-spine, known in its isolated 

 state as MyriacantJms granulatus, and (ii.) a dentition whicli, 

 if found separately, would be described as a species of Fro- 

 gnathodus. Of these names that applied to the dorsal fin-spine 

 is much the earliest, and the small species described by Eger- 

 ton must thus be known as Myriacanthus granulatws. 



The denlition of Myriacanthus granulatus only attains one 

 half the size of that named Prognathodus Guentheri] and 

 there need be no hesitation in associating with the latter 

 " species " the group of teeth described as Ischyodus John- 

 sou i by Agassiz *. Moreover, it may be noted that the larger 

 type differs specifically from the smaller in the form of the 

 presymphysial mandibular tooth, the outer face of this ele- 

 ment being gently rounded in the former type and longitu- 

 dinally angulated in the latter, while in the first the inner 

 layer of dentine also exhibits the greatest development. 



Now it is interesting to note that the typical species of 

 Myriacanthus (J/, paradoxus f) attains at least twice the size 

 of M. granulatus, the basal portion of a very large spine of 

 this form having been named M. retrorsus by Agassiz \, and 

 fine examples being preserved in the British Museum. If 

 ^^Prognathodus " is the dentition of one species, it also presu- 

 mably characterizes the other ; and the relative proportions of 

 spines and teeth agreeing precisely, it may be inferred that, 

 just as the smaller dentition pertains to Myriacanthus granu- 

 latus, so is the larger Prognathodus Guentheri [^Ischyodus 

 Johnsoni) referable to M. jparadoxus. 



Such being the case, the genus Myriacanthus may be 

 removed from the Ichthyodorulites and placed in a definite 

 position among the Chimaroid fishes ; and to include both 

 this and the closely allied Chimcero2)sis oi \\\q Bavarian Litho- 

 graphic Stone § it seems necessary to institute a new family 

 as follows : — 



Myriacanthidse. 



Body elongate ; anterior dorsal fin above the pectorals, 

 provided with a long, straight, robust spine. Teeth forming 



* Op. cit. vol. iii. (184^), p. 344, pi. xl. c. fig. 22. 



t Ibid. vol. i. (1837), p. 38, pi. vi. 



X Tom. cit. (1837), p. 39, pi. viii,«. figs. 14, 15. 



§ K. A. von Zittel, op. cit. vol. iii. (1887), p. 113, woodc. f. 126. .1. 

 Hiess, " Ueber einig-e fossile Chim8eriden-Keste," PakeoutogT. vol. xxxiv. 

 (1887), p. 21, pi. ii. ligs, U 11,, pi. iii. tigs. 1-10. 



