﻿CHIM^KID-ffl. 59 



P. 2846-7. One of the type specimens of Leptacanthus semistriatus, 

 Agassiz, figured, in the Poiss. Foss. vol. iii. pi. vii. fig. 6 ; 

 also two larger portions of similar spines. 



Enniskillen Coll. 



47975-77. Portions of three similar spines. 



Presented by the Hon. Robert Marsham, 1877. 



P. 251. Abraded spine of the same " species." 



Presented by J. Wood-Mason, Esq. 1880. 



P. 2213. Two nearly complete similar spines. Egerton Coll. 



P. 4173. Impression of a similar spine labelled by Agassiz thns : — 

 " Peut-etre le rayon du Psammodus magnus ; decrit sous 

 le nom de Leptacanthus semistriatus." Enniskillen Coll. 



P. 3108. Type specimen of Leptacanthus serratus, Agassiz, described 

 and figured in the Poiss. Foss. vol. iii. (1837), p. 29, 

 pi. vii. fig. 1. Enniskillen Coll. 



28596. Portion of distal half of a similar spine; Eyeford, near 

 Naunton, Gloucestershire. Purchased, 1853. 



P. 6222. Crushed portion of a similar spine. 



Genus ISCHYODUS, Egerton. 



[Proc. Geol. Soc. vol. iv. 1843, p. 155.] 



Syn. Leptacanthus, L. Agassiz, Poiss, Foss. vol. iii. 1837, p. 27 (in part). 

 Auluxacanthus, H. E. Sauvage, Catal. Poiss. Form. Second. Bou- 



lonnais (Mem. Soc. Acad. Boulogne, vol. ii.), 1867, p. 63. 

 Chimcer acanthus, F. A. Quenstedt, Der Jura, 1858, p. 347. 



Mandibular tooth more or less massive, with a well-defined hard 

 layer upon the outer aspect immediately below the oral margin ; one 

 anterior tritor usually present, sometimes several; one median 

 tritor, and two or more external tritors. Palatine tooth very robust, 

 with a well-defined hard layer upon the outer aspect immediately 

 above the oral margin ; four tritors present, two being inner, one 

 median, and one outer. Vomerine tooth more or less quadrate in 

 side view, with tritors upon the oral margin ; post-oral region not 

 laterally expanded, and usually with a definite hard thickening. 

 Dorsal fin-spine laterally compressed, smooth or longitudinally 

 striated, with a double series of posterior denticles. Head-spine of 

 male short, arched, with a terminal cluster of denticles. 



