SUB-CLASS V 



( JANOIDEI 



73 



Macropoma, Ag. Maxilla, vomer, and palatine with conical teeth. Sup- 

 plementary caudal fin unknown. Fin rays robust and straight, not expanded 

 distally, with distant articulations ; a double series of small, upwardly pointing 

 denticles on nearly all the rays of the first dorsal and caudal fins. Turonian 

 and Senonian of Europe. M. mantelli, Ag., especially well preserved in the 

 English Chalk. 



Family 5. Polypteridae. Huxley. 



Body covered with thick, rhombic ganoid scales. Vertebrae and the complete 

 internal skeleton ossified. Tail diphycercal. Pectoral fins with short, obtuse lobe, 

 the numerous, short, fan-like basalia attached to two diverging bones (propterygium 

 and metapferygium) and a median mesopterygium. Dorsal fin single, remarkably 

 extended, the spine-like rays borne by a corresponding number of supports. Only a 

 single pair of jugular 



plates. Teeth sharply ^^s^^M^^^^^^MMt 



conical, with simple pulp 

 cavity. Recent. 



Fig. 132. 

 Polyptcrus bicMr, Geottr. Recent ; Upper Nile. 



To this family be- 

 long the two genera, 

 Polypterus (Fig. 132) and Calamoichthys, living in the rivers of tropical Africa. 



Order 2. CHONDROSTEI. Cartilaginous Ganoids. 



Notochord persistent, and endoskeleton chiefly cartilaginous ; head covered with 

 bony dermal plates. Teeth small or wanting. Opercular apparatus imperfectly 

 developed, the branchiostegal rays usually absent. Infraclavicle present. Paired 

 fins without a scaly axis, but each pelvic fin with a row of cartilaginous basal supports. 

 A single dorsal and anal fin, with dermal rays more numerous than their supports. 

 Caudal fin heterocercal (rarely diphycercal), and the upper lobe usually covered with 

 rhombic scales. Trunk almost or completely naked, or with rows of bony plates. 



Family 1. Chondrosteidae. Smith Woodward. 1 



Parietal and frontal bones paired ; a large squamosal bordering the parietal s on 

 each side. Jaws toothless, and premaxilla absent. Operculum small, suboperculum 

 large ; a few branchiostegal rays present. Trunk naked, only the upper fulcrated 

 lobe of the tail with elongated, oat-shaped ganoid scales. Lias. 



Chondrosteus, Egerton. Mouth very small and inferior ; jaws toothless ; 

 maxilla arched, much expanded behind and tapering in front. About ten 

 branchiostegal rays, but no gular plate. Dorsal fin short-based, opposed to 

 the pelvic pair. Trunk naked. C. acipenseroides, Eg., about a metre in 

 length, known by nearly complete skeletons from the Lower Lias of England. 



Gyrosteus, Sm. Woodward (ex Ag. MS.). Usually much larger than 

 Chondrosteus, and the toothless maxilla expanded in its front portion for a 

 palatine articulation. G. mirabilis, Sm. Woodw. (ex Agassiz, MS.), represented 

 by fragments in the Upper Lias of Whitby. 



1 Woodward, A. S., On the Palaeontology of Sturgeons (Proc. Geol. Assoc, vol. XL), 1889 ; 

 also Proc. Yorks. Geol. and Polyt. Soc. vol. XIII. 1898, p. 461. 



