DISTICHODUS. 



139 



6. DISTICHODUS. 



Muller & Troschel, Hor. Ichthyol. i. p. 12 (1845) ; Cuvier & Valenciennes, Hist. Poiss. xxii. p. 172 

 (1849) ; Giinther, Cat. Fish. v. p. 359 (1864) ; Bonlenger, Poiss. Bass. Congo, p. 185 

 (1901). 



Mouth small, inferior or subinfericr, with small bicuspid teeth, usually forming- 

 two series in each jaw ; maxillary toothless, moderately large. Cheek covered by the 

 suborbitals ; nostrils close together, separated by a valvular flap ; gill-membranes 

 attached to the isthmus ; 4 branchiostegal rays. Body short or moderately elongate, 

 strongly compressed; belly rounded. Scales moderate or small, with strongly ciliated 

 border; lateral line equally distant from the dorsal and the ventral outlines, or nearer 

 the former ; a scaly process at the base of the ventral fin. Dorsal fin with 16 to 27 

 rays, above the ventrals ; anal fin with 11 to 21 rays ; a small or moderately large 

 adipose dorsal fin. 



The scales are bordered by a fringe of long, closely-set spines ; the tubules of the 

 lateral line are perfectly straight. Small scales cover the whole or the greater part 



Pig. 21. 



Jaws and lateral scales of Disticlwdus niloticus. 



of the caudal and adipose fins. The pectoral fin is composed of 18 to 20 rays, the 

 ventral of 11 or 12. 



In this genus, as in Citharinus, the brain-case extends forwards between the orbits, 

 a character which is constant throughout the Cyprinidse. An elongate fontanelle, 

 beginning between the orbits, separates the frontal and parietal bones on the median 

 line ; the supraorbital bone is absent and the supraoccipital bears a more or less 

 elevated crest. The vertebrae number 44 to 51 (27-33 + 17-18) : D. niloticus has 

 33 + 18. 



t2 



