Ga n oidei — Crossop terygidce. 



21 



Ceratodus are abundant in the Trias and Rhaetic. The other genera 

 are Palcedaphus, ITeliodus, Phaneropleuron (Fig. 46), from the Old 

 Red Sandstone, and Uroiiemus, Ganoprislodus, from the Carboni- 

 ferous rocks. (See Figs. 44, 45.) 



Fig. 46. — Restoration of Phaneropleuron (after Traquair). 



Order Y.— GANOIDEI * 



The fishes of this order are, in most instances, covered with 

 osseous ganoid scales or scutes — the pelvic fins are always 

 abdominal. 



The skeleton in some is notochordal, or cartilaginous, in others 

 partially or completely ossified. 



Fig. 47.— The African Mudfish, Protopterus annectens, living in the rivers of Africa. 



Only one external gill-opening exists on each side, protected by 

 a gill- cover. 



Among living Ganoids there are four well-marked types : — 



Suborder I. — Crossopterygid^j. 



The Crossopteryyida, which are represented by Polypterus (Fig. 

 48) and Calamoichthjs, are confined to the rivers of tropical Africa 

 (especially those of the West coast) and the Upper Nile. 



Fig. 48 —Polypterus bichir, living in the Nile, Gamhia, etc. 

 a, pectoral fin ; b, pelvic fin; c, anal fin. 



* Three previously-noticed groups — Acanthodini, Placodermata, and Cephal- 

 aspidce— are sometimes classed under the Ganoidei : from the remarks of Prof. 

 Huxley, Dr. R. H. Traquair, Prof. E. D. Cope, and others, it seems quite 

 probable that these ancient types of fishes may hereafter form more than one 

 distinct order. 



