﻿4 ACANTHODTI. 



Family ACANTHODID^E. 



A single dorsal fin present, both this and the anal with an 

 anterior spine. Clavicular bones absent. 



Synopsis of Genera. 



A. Teeth minute or absent. 



Dorsal fin not in advance of anal Acantkodes (p. 2). 



Dorsal fin in advance of anal Cheiracanthus (p. 16). 



B. Teeth large. 



[Arrangement of fins unknown.] Acanthodopsis (p. 15). 



Genus ACANTKODES, Agassiz. 



[Poiss. Foss. vol. ii. pt. i. 1833, p. 19.] 



Syn. Acanthoessus, L. Agassiz, Neues Jahrb. 1832, p. 149. 



Holacanthodes, E. Beyrich, Monatsb. Berl. Akad. 1848, p. 24. 

 Mesacanthus, K. H. Traquair, Geol. Mag. [3] vol. v. 1888, p. 511. 



Body elongate, tapering, and laterally compressed. Teeth minute 

 or absent ; orbit with ring of four circumorbital plates. Pectoral 

 fins very large ; pelvic pair smaller. Dorsal fin remote, never 

 arising in advance of a point opposite the anal fin-spine. 



, Fig. 1. 



Restoration of Acantkodes wardi, Egert. — Coal-Measures, England and 

 Scotland. 



This, the type genus of the family and order, has been more 

 thoroughly investigated than any of the allied genera \ It thus 

 seems advisable to summarize the known facts in the anatomy of the 

 fish, and compare some of its more striking features with those pre- 

 sented by certain members of the Diplacanth family. 



In the head, the suspensorium is oblique and the gape of the 

 mouth correspondingly wide. The orbit is placed far forwards, and 

 the upper jaw evidently projects somewhat in advance of the lower. 

 The cartilage of the cranium and jaws is partially strengthened by 



1 See especially the memoirs of Roetner and Kner, quoted in the synonymy 

 of A. hrovni. 



