424 



PAKENTAL CAKE AMONG FRESH-WATEK FISHES. 



THE BICHIRS. 



The family of Polypterids or Bichirs is peculiarly interesting, as, 

 to a greater extent than any other recent group, it is intermediate 

 between fishes and amj^hibians — that is, betAveen vertebrates having 

 fins and those with legs. The body is more or less elongated or sub- 

 cylindrical and covered with ol)lique rows of enameled rhombic 

 scales; the head is snakelike and protected by bony plates; the caudal 

 fin rounded and continuous upward and forward with the dorsal fin; 

 the dorjs^Ji furniture is especially remarkable; there are along most of 

 the length of the back a row of spines (very different from the 

 spines of other fishes) Avith whose hinder surfaces generally several 

 raylike appendages articulate and a membrane is developed, thus 

 resembling separate finlets. The anal is small and almost continuous 

 with the caudal fin, and the ventrals are also far back ; the pectorals 

 are rounded and most prominent below the middle of the hinder 

 margin. 



The family has two very distinct genera — PolypteriiH and Cala- 

 michthys. Of the former one or more of 10 species are found every- 



PoUjptcnis hicliir. After Geoffrey Saint-Ililaire. 



where in tropical Africa ; of the latter only one — a very elongated, 

 eel-like form without ventral fins — occurs in a few rivers of Avestern 

 Africa. 



The species of Polypterus are so much alike that they have been 

 supposed by some to be variants of one species, but they are really 

 Avell distinguished by differences in the number of dorsal spines 

 (ranging from 5 to 18), size of scales, size of eyes, and other charac- 

 ters. The oldest knoAvn species (it Avas knoAvn to the ancient Egyp- 

 tians, but Avas first described by Geoffroy Saint-Hilaire in 1809) is 

 at one extreme Avith 15 to 18 spines, and one, described by W. O. 

 Ayers, of Boston, in 1850, is at the other extreme, Avith 5 to 8 spines. 



The habits of the Polypterids are characteristic. They are in the 

 main bottom fishes and lethargic. But they are not confined to such 

 places and conditions. Harrington found that they also live " in 

 the deeper depressions of the muddy riA'er bed," and there they are 

 •' active '' swimmers and " not essentially bottom-liA^ers or mudfishes." 

 They are most active at nighttime, Avhen " in search of food." But 

 in shalloAv Avater they Avill lie for long periods on the mud at the 

 bottom of the Avater, with the body a little upraised forward and 



