﻿MYRIACANTHID.E. 49 



Myriacanthus granulatus, Agassiz. 



[Plate II. fig. 4; Plate III. figs. 3, 4.] 



1887. Myriacanthus granulatus, L. Agassiz, Poiss. Foss. vol. iii. p. 40, 



pi. viii. a. fig. 16. 

 1837. Leptacanthus tenuispinus, L. Agassiz, ibid. p. 27, pi. i. figs. 12, 13. 



[Spine ; British Museum.] 

 1871. Ischyodus orthorhinus, Sir P. Egerton, Quart. Journ. Geol. Soc. 



vol. xxvii. p. 275, pi. xiii. [Head, &c. ; British Museum.] 

 1887. Metopacanthus orthorhinus, K. A. von Zittel, Handb. Palaeont. 



vol. iii. p. 111. 

 1889. Myriacanthus granulatus, A. S. Woodward, Ann. Mag. Nat. 



Hist. [6] vol. iv. p. 279. 



Type. Imperfect dorsal fin-spine ; British Museum. 



A species of comparatively small size, the dorsal spine attaining 

 a maximum length of about 0*18. Dorsal spine much laterally- 

 compressed, with an acute anterior edge ; lateral tubercles relatively 

 small and closely arranged, absent upon a long extent from the 

 much attenuated apex ; anterior and posterior denticles long, com- 

 paratively slender, and closely arranged ; a long series of the pos- 

 terior denticles distally directed downwards, the others pointing 

 upwards. Maximum thickness of presymphysial tooth about one 

 third its breadth, and the tritor confined to a narrow median 

 band, lenticular in section ; outer face of the tooth strongly convex, 

 with a sharply rounded, median, longitudinal elevation, the inner 

 face equally concave. 



This is the type species of the so-called Metopacanthus. 



Form. Sf Log. Lower Lias : Lyme Regis, Dorsetshire. 



43050. Head and associated dorsal fin-spine in position, described 

 and figured by Egerton, he. cit., as the type specimen of 

 Ischyodus orthorhinus, and subsequently adopted as the 

 type of Metopacanthus by Zittel, loc. cit. The rostral spine 

 is shown to be covered superiorly with granulations, finer 

 and more closely arranged than those of the sides of the 

 dorsal spine. Purchased, 1871. 



P. 4575. Remains of the head with dentition, and the basal half of 

 the rostral spine ; also a fragment of the dorsal spine, 

 probably found associated. The jaws and a few dermal 

 tubercles are shown, of the natural size, in PL II. fig. 4, 

 and the parts are indicated by the lettering. A portion of 

 the cartilage of the mandible is seen from the outer ante- 

 rior aspect ; and overlapping the oral margin is observed 

 the pair of large mandibular teeth (rnd.). Immediately 



PART II. e 



