﻿394 CR0SS0PTER5TGII. 



Suborder III. ACTINISTIA. 



Notochord persistent. Axonosts of each of the dorsal and anal 

 fins fused into a single piece ; a series of axonosts, equal in number 

 to the supporting neural and haemal spines, present in the caudal 

 fin above and below, each axonost directly connected with a single 

 dermal fin-ray. Axonost of pelvic fin on each side single, the right 

 and left not fused together mesially. 



Of this suborder only one family, that of the Coelacanthidae, is 

 at present known. 



Family CCELACANTHID^E. 



Body deeply and irregularly fusiform, with cycloidal, deeply- 

 overlapping scales, more or less ornamented wibh ganoine. Branchi- 

 ostegal apparatus consisting of an operculum on each side and a 

 single pair of large jugular plates. Paired fins obtusely lobate. 

 Two dorsal fins and a single anal; the anterior dorsal without 

 baseosts, the posterior dorsal and the anal with baseosts, obtusely 

 lobate. Axial skeleton extending to the extremity of the caudal 

 fin, usually projecting and terminated by a small supplementary 

 caudal fin. Air-bladder ossified. 



As in many other primitive types of fishes, the arches and spines 

 of the axial skeleton in this family are only superficially ossified, 

 thus appearing, in the fossilized state, as if originally hollow. Such 

 an appearance suggested the name of Coelacanthidae to Agassiz, 

 who used the term in a wide and somewhat indefinite sense. The 

 first scientific definition of the family was given by Huxley in 

 1861 and 1866. 



The most satisfactory information concerning the osteology of 

 the Coelacanthidae is afforded by remains from the Chalk of Eng- 

 land and the Lithographic Stone of Bavaria. Macropoma, from 

 the Chalk, is described in detail by Huxley \ chiefly from specimens 

 recorded below ; while the genera of the Lithographic Stone are 

 elucidated by Reis in a recently published memoir 2 . Undina gulo, 

 from the English Lias, is also often well preserved, and a restora- 

 tion of the skeleton is given in fig. 53, p. 412. 



1 T. H. Huxley, " Illustrations of the Structure of the Crossopterygian 

 Ganoids " (Mem. Geol. Surv. dec. xii. 1866). 



2 O. M. Reis, " Die Ccelacanthinen, mit besonderer Beriicksichtigung der im 

 Weissen Jura Bayerns vorkommenden Gattungen" (Palaeontographica, vol. 

 xxxv. 1888). 



