98 CHAEACINID^. 



III. DISTICHODONTIN.E. — Teeth small, bicuspid ; maxillary well developed ; scales ciliated ; 

 lateral line median. 



Gill-membranes free from isthmus ; small teeth at the base of the 



maxillary 5. Nanncethiops, Gthr. 



Gill-membranes attached to isthmus ; maxillary toothless ; dorsal fin 



with 16 rays or more 6. Distichodus,M. & T. 



Gill-membranes attached to isthmus ; maxillary toothless ; dorsal fin with 



not more than 15 rays 7. Nannocharax, Gthr. 



IV. Citharinin^. — Teeth minute, unicuspid ; maxillary small ; scales not ciliated ; lateral fine 

 median. 



Gill-membranes free from isthmus ; body very deep, very strongly 



compressed 8. Citliarinus, Guv. 



1. HYDROCYON, 



Hydrocinus, part., Cuvier, Regne Anim. ii. p. 167 (1817). 



Hydrocyon, Cuvier, Mem. Mus. Paris, v. 1819, p. 353 ; Cuvier & Valenciennes, Hist. Poiss. xxii. 



p. 309 (1849) ; Gtinther, Gat. Fish. v. p. 350 (1861) ; Boulenger, Poiss. Bass. Congo, p. 140 



(1901). 



Snout rather elongate ; mouth large, with very strong, pointed, more or less 

 compressed, sharp-edged teeth, wide apart and forming a single series; prsemaxillary 

 bones slightly movable vertically ; maxillary toothless, moderately large, and slipping 

 under the praeorbital. Cheek covered by the large suborbitals ; nostrils near the eye, 

 close together, separated by a valvular flap ; gill-membranes free from the isthmus ; 

 4 bran chios legal rays. Body elongate, compressed ; belly rounded. Scales moderately 

 large, not ciliated ; lateral line nearer the ventral than the dorsal outline ; a scaly 

 process at the base of the ventral fin. Dorsal fin with 10 or 11 rays, above the 

 ventrals ; anal with 13 to 18 rays ; a small adipose dorsal fin. 



Part of the eye, in front and behind, is covered by an adipose eyelid. The tubules 

 of the lateral line are straight and short, and most of them emit a short spur, directed 

 downwards, or a few scales here and there having the spur directed upwards. The 

 fins are more or less falcate; the rays of the pectoral are 15 or 16 in number, those of 

 the ventrals 10. 



The skull is strongly ossified ; the supraorbital bone is large ; an elongate fontanelle 

 separates the parietals and the posterior part of the frontals in the young, but closes up 

 with age ; a supraoccipital crest is present ; the brain-case does not extend far forwards, 

 an interorbital septum being present. The pramaxillaries are much larger than the 

 maxillaries, to which they are ankylosed ; there are 4 to 6 large teeth on the former 



