150 



CHAEACINIDJE. 



7. NANNOCHARAX. 

 Giinther, Ann. & Mag. N. H. (3) xx. 1867, p. 112 ; Boulenger, Poiss. Bass. Congo, p. 196 (1901). 



Mouth very small, inferior, each jaw with a single series of small, notched, bicuspid 

 teeth; maxillary toothless, moderately large. Cheek covered by the suborbitals ; 

 nostrils close together, near the eye, separated by a valvular flap ; gill-membranes free 

 on the sides only ; 4 branchiostegal rays. Body more or less elongate, cylindrical or 

 feebly compressed. Scales small, with strongly ciliated border ; lateral line equally 

 distant from the dorsal and the ventral outlines ; a scaly process at the base of the 

 ventral fin. Dorsal fin with 12 to 15 rays, above the ventral s ; anal fin with 10 or 

 11 rays; a small adipose dorsal fin. 



A narrow fontanelle separates the parietals and extends forwards between the 

 frontals; the supraorbital bone is absent. The vertebrae number 44 (22 + 22) in 

 N. niloticus, 43 (21+22) in N. elongatus from the Congo. 



The air-bladder, as noticed by Mr. Eowntree, is much reduced. It does not 

 extend more than half the length of the body-cavity. There is the usual division into 

 two chambers, of which the posterior is considerably the longer, but the cavities 

 appear to be largely obliterated. The anterior chamber is globular, with hard tough 

 walls, the posterior is narrowed almost to a rudiment. The digestive canal is about as 

 long as the whole fish. 



This genus, which may be described as a dwarfed modification of Bistichodus, 

 embraces six small species : — One from the Nile, one from the Gaboon and the Congo 

 (1S T . fasciatus, Gthr.), three from the Congo (N. brevis^ Blgr., W. elongatus, Blgr., and 

 N. tcenia, Blgr.), and one from Cameroon (N. intermedins, Blgr.). 



1. NANNOCHARAX NILOTICUS. 

 (Plate XXI. fig. 4.) 



Core g onus niloticus, Joannis, Mag. Zool. 1835, iv. pi. vii. 



Nannocharax niloticus, Giinther, Ann. & Mag. N. H. (3) xx. 1867, p. 113 ; Boulenger, Poiss. Bass. 

 Congo, p. 198 (1901). 



Depth of body five to six times in the total length, length of head four to five times. 

 Head once and three-fourths to twice as long as broad, as deep as broad; snout 

 rounded, nearly as long as or a little shorter than the eye, the diameter of which is 

 contained three times or nearly three times in the length of the head ; interorbital 

 width slightly less than the diameter of the eye. Gill-rakers short, 8 to 10 on the 



