POLYPTEEIDyE. 



1. POLYPTERUS. 



Geofr*roy, Ann. Mus. Paris, i. 1802, p. 57, and Descr. Egypte, Poiss. p. 4 (1809) ; A. Dumeril, Hist. 

 Poiss. ii. p. 391 (1870) ; Boulenger, Poiss. Bass. Congo, p. 20 (1901). 



Body more or less elongate, not serpentiform ; spines of the dorsal fin bearing 

 several articulated rays ; ventral fins present ; suboperculum present. 



Polypterus is represented in the Nile and the principal river-systems of tropical 

 Africa, with, the exception of the Zambesi ; also in Lake Chad, Lake Rudolf, and 

 Lake Tanganyika. 10 species are distinguished: — 



1. P. bichir, Geoffr. — Nile, L. Rudolf, Chad Basin. 

 2» P. lapradii, Stdr. — Senegal, Gambia, Niger. 



3. P. congicus, Blgr. — Congo, L. Tanganyika. 



4. P. endlicheri, Heck. — Nile, Niger, Chad Basin. 



5. P. ornatipinnis, Blgr. — Congo. 



6. P. delhezi, Blgr. — Congo. 



7. P. weehii, Blgr. — Congo. 



8. P. senegalus, Cuv. — Nile, L. Rudolf, Chad Basin, Senegal, Gambia, Niger. 



9. P. palmas, Ay res. — Guinea, Congo. 

 10. P. retropinnis, Vaill. — Congo. 



The number of dorsal spines varies in each species, but within moderate limits ; 

 thus, in the species in which they are least numerous, P. palmas, the ascertained 

 range of variation is from 5 to 8, whilst in P. bichir, which has the highest number, 

 the range is from 14 to 18. The articulated rays borne by each spine vary from 4 

 to 7 in P. bichir and P. senegalus, from 5 to 9 in P. endlicheri. 



The sexes are distinguished externally by the form of the anal fin, which, in the 

 males, has the anterior rays much thickened, whilst the scaly fold at its base is also 

 enlarged. The difference in the appearance of the fin is shown on PI. III., the upper 

 figure (skeleton) being that of a male, the lower that of a female; also on figs. 1 

 and 2 (p. 3), the former representing a female, the latter a male. This difference 

 in the outer form of the anal is accompanied by an internal one, the anterior 

 endoskeletal supports of this fin being fused in the males into a single triracliate 

 bone, as represented on PI. III., upper figure. 



As a rule, there is a very distinct gap between the anal fin and the caudal ; but in 

 a specimen of P. senegalus from Fashoda, which is here figured (fig. 1), the gap is 

 filled by what appears to be a second anal fin, with seven slender rays. The caudal 

 fin, which is normally symmetrical, sometimes exhibits a tendency to heterocercy ; 

 the most pronounced case of this kind with which I have come across occurs in a 

 P. senegalus, likewise from Fashoda, of which a figure is also given (fig. 2). 



