H2 CHABAOINIDiE. 



(A. dentex and A. baremose) with the anterior supraorbital bone very narrow and with 

 a large fontanelle separating the parietals and the frontals posteriorly ; the other 

 (A. nurse and A. macrolepidotus) with both supraorbital bones large and no fontanelle. 

 The vertebral column contains 37 to 51 vertebrae, the numbers of prsecaudals and 

 caudals being as follows in the Nile species: — 



A.dentex 22 or 23 + 20 or 21 = 42-44. 



A. baremose 25 to 28 + 23 or 24 = 49-51. 



A. nurse 23 + 16 = 39. 



A. macrolepidotus 26 + 16 = 42. 



In A. dentex and A. baremose the posterior chamber of the air-bladder is about 

 four times as long as the anterior and extends backwards into the caudal region, 

 almost to the root of the caudal fin, on the right side of the interheemals of the anal 

 fin, or sometimes on the left. In A. nurse and A. macrolepidotus the posterior 

 chamber is to the anterior as 3 : 2 or 2:1, and it does not extend beyond the body- 

 cavity. The pyloric appendages of the stomach are large, 10 to 14 in number. 

 The intestine is usually a little shorter than the whole fish in the species which 

 feed principally on animal prey (small fish, crustaceans, insects, &c), but in 

 A. macrolepidotus, which is mainly a vegetarian, it is considerably longer, about as 7 : 5. 



The genus Alestes is represented by twenty-eight species in the fresh waters of 

 Africa, from the Nile to the Zambesi and Natal and from the Senegal to the Congo. 

 Five species are known to occur in the Nile system. 



I. Scales 44-51 in the lateral line, -\~ in a transverse series ; dorsal fin behind vertical of 



on 



Synopsis of the Species 



-n 



fj A 111 L11C ltXLClCll 1111C, 1 



ventrals. 

 Dorsal originating just behind vertical of last ray of ventral ; anal 



III 19-23 ; 20-26 gill- rakers on lower part of anterior arch . 1. A. denies, L. 

 Dorsal equidistant from vertical of last ray of ventral and first ray 



of anal, or a little nearer the latter ; anal III 22-27 ; 30-38 



gill-rakers on lower part of anterior arch 2. A. baremose, Joannis. 



II. Scales 22 to 33 in the lateral line, *~ ( \ in a transverse series. 



Dorsal originating just behind vertical of ventrals, equally distant 

 from occiput and from caudal fin ; anal III 16-17 ; scales 

 33 — 3. A. sadleri, Blgr. 



Dorsal originating above root of ventrals, nearer occiput than caudal 



fin ; anal III 11-15 ; scales 26-33 S • 4. A. nurse, Eiipp. 



°2 



Dorsal above middle of space between ventrals and anal, nearer 



eaudal fin than occiput ; anal III 12-14 ; scales 22-26 ^r^r . 5. A. macrolepidotus, C. & V. 



