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 suboperculum are present. 
Ten species are known, of which six pertain to the Congo and 
its tributaries! 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? on the widely distributed P. 
senegalus and those of Harrington ® on P. bichir, have brought to 
light many interesting facts about these most interesting Fishes. 
ee 
——— 
eo 
Fic. 279.—Polypterus senegalus. -From a specimen in the Cambridge University 
Museum. The arrow points to the position of the left spiracle. x 3. 
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. JP. bichir 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 seg.; 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, 
Pp. LL: 
3 Amer. Nat. xxxiii. 1899, p. 721; Science (2), ix. 1899, p. 314. 
