482 FISHES CHAP. 



surviving family of Crossopterygii, the Polypteridae, are restricted 

 to the Nile and to the river basins of tropical Africa which drain 

 into the Atlantic (Fig. 280). Only two genera are known, 

 Polypterus and Calamichthys, neither of which has yet been dis- 

 covered in any geological deposits, ancient or recent. 



In Polypterus each of the spines of the dorsal fin supports 

 several soft rays. Pelvic fins and a suboperculuin are present. 

 Ten species are known, of which six pertain to the Congo and 

 its tributaries. 1 P. bichir is said to attain a length of four 

 feet. 



Until recently little was known of the habits of Polypterus, 

 but the observations of Budgett 2 on the widely distributed P. 

 senegalus and those of Harrington 3 on P. bichir, have brought to 

 light many interesting facts about these most interesting Fishes. 



FIG. 279. Polypterus senegalus. From a specimen in the Cambridge University 

 Museum. The arrow points to the position of the left spiracle, x ^. 



P. bichir haunts the deeper holes and depressions of the 

 muddy bed of the Nile, although it is " not essentially a bottom- 

 liver or a mud-fish." It is most active at night when in search 

 of food, and then it may readily be taken by trawl lines. The 

 lobate pectoral fins are used for progression, but their primary 

 function is to act as balancers, and they exhibit the characteristic 

 trembling movements so often seen in the balancing fins of 

 Teleosts. Polypterus does not readily live out of water, rarely 

 longer than three to four hours, and then only when covered 

 with damp grass or weeds. P. lichir is said to feed on small 

 Teleosts, which it swallows whole, and to these there may be 

 added in other species, Batrachians and Crustaceans. The 

 observations of Budgett show that in captivity Polypterus often 

 remains motionless for a long time at the bottom of the water, 

 the anterior part of the body resting upon the tips of the 



1 Boulenger, op. cit. p. 20 et seq. ; id. Ann. Mus. Congo, Zool. (1), i. Fasc. 4, 

 Bruxelles, 1899, p. 61 ; ii. Fasc. 2, 1902, p. 23. 



2 Proc. Camb. Phil. Soc. x. 1900, p. 236 ; Trans. Zool. Soc. xvi. Pt. ii. 1901, 

 p. 115. 



3 Amer. Nat. xxxiii. 1899, p. 721 ; Science (2), ix. 1899, p. 314. 



