Mr. A. 8. Woodward on the Myriacanthide. 279 
present writer to justify the assertion of the generic identity: 
of these two fishes. 
The so-called Ischyodus (or Metopacanthus) orthorhinus 
thus possesses (i.) a dorsal fin-spine, known in its isolated 
state as Myriacanthus granulatus, and (ii.) a dentition which, 
if found separately, would be described as a species of Pro- 
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 granulatus. 
The dentition of Myriacanthus granulatus only attains one 
half the size of that named Prognathodus Guenthert; and 
there need be no hesitation in associating with the latter 
““ species” the group of teeth described as Ischyodus John- 
sont 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 (M. paradoxus Tt) attains at least twice the size 
of MW. granulatus, the basal portion of a very large spine of 
this form having been named J. retrorsus by Agassiz ft, 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 
Johnsont) referable to MM. paradoxus. 
Such being the case, the genus Myriacanthus may be 
removed from the Ichthyodorulites and placed in a definite 
position among the Chimeeroid fishes; and to include both 
this and the closely allied Chimeropsis of the Bavarian Litho- 
graphic Stone§ it seems necessary to institute a new family 
_ as follows :— 
Myriacanthide. 
Body elongate; anterior dorsal fin above the pectorals, 
provided with a long, straight, robust spine. Teeth forming 
* Op. cit. vol. iii. (1843), p. 344, pl. xl. e. fig. 22. 
+ Ibid. vol. i. (1837), p. 38, pl. vi. . 
{ Tom. cit. (1837), p. 89, pl. viil.a. figs. 14, 15. 
§ K. A, von Zittel, op. cit. vol. iii. (1887), p. 115, woode. f. 126. J. 
Riess, “‘ Ueber einige fossile Chimeriden-Reste,” Paleeontogy. vol. xxxiy. 
(1887), p. 21, pl. ii. figs. 9-11, pl. iii. figs. 1-10. 
