140 CHARACINIDJE. 



The air-bladder is large, the posterior chamber about five times as long as the 

 anterior, the outer membrane of which is in communication with the skin, at the 

 beginning of the lateral line, by a rather large meatus, filled with a gelatinous 

 substance, between the dorsal and ventral lateral muscles*. The intestine is nearly 

 three times as long as the whole fish and forms numerous coils ; it is usually full of 

 soft mud and decomposed vegetable matter. 



This very natural genus, the range of which extends over the whole of tropical 

 Africa (with the exception of Lakes Victoria and Tanganyika) and the Nile, comprises 

 seventeen species ; a synopsis of these has been given by me in the ' Annals and 

 Magazine of Natural History,' (7) viii. 1901, p. 510. Four species occur in the 

 Nile system. 



Synopsis of the Species. 



I. Snout not compressed, its length less than the interorbital width ; width of mouth three to 



four and two-thirds times in length of head ; lobes of caudal fin rounded or obtusely 

 pointed, 



A. Interorbital width considerably less than half length of head ; base of adipose fin not more 



than half as long as its distance from the rayed dorsal, which is composed of 22 to 

 26 rays. 

 Scales 90-110 a ~~ . 15-18 betweeen lateral line and ventral . . . . 1. D. niloticus, L. 



20-25' 



Scales 83-98 i|=|? 13-15 between lateral line and ventral 2. B. rostratus, Gthr. 



B. Interorbital width half, or a little less than half length of head ; base of adipose fin 



as long as or a little shorter than its distance from the rayed dorsal, which is composed 

 of 20 to 23 rays. 

 Scales 80-91 jgPjF, 18-20 between lateral line and ventral 3. D. brevipinnis, Gthr. 



II. Snout compressed, projecting very strongly beyond the mouth, its length equalling, or nearly 



equalling, interorbital width ; width of mouth five to six times in length of head ; lobes 

 of caudal fin acutely pointed. 

 Scales 75-85 {|rpt 11 or 12 between lateral line and ventral . . . . 4. JD. engi/cejjhalus, Gthr. 



The supposed fifth species from the White Nile, described by Dr. Steindachner as 

 Distichodus marnoi, is, as I have already pointed out, based on a young specimen of 

 Citharinus citharus. 



* A feature also met with in some Loaches and Cat-Fishes. 



