4 POLYPTERIDJE. 



Three such specimens of P. Mchir, from near Cairo, have been presented to the 

 British Museum by Dr. J. C. Mitchell, and two specimens, belonging to P. senegalus, 

 have been found by Mr. Loat in the White Nile. 



The specimens with external gills at present known may be arranged in three 

 divisions: — (1) Without scales, and with the dorsal fin spineless, not differentiated 



Pig. 3. 





Larval specimen of P. senegalus (after Budgett). x 3|. 



from the caudal ; the only example known being the larval specimen of P. senegalus 

 brought home from the Gambia by the late Mr. Budgett, and described and figured 

 by him. (2) With scales of a cycloid type and with the dorsal fin as in the preceding. 

 (3) With all the essential characters of the mature form. 



The scales, when they first appear, are very thin, circular, juxtaposed, and only well 

 developed about the lateral line and on the tail. Though devoid of spines, and in no 



Fig. 4. 



Young specimen of P. senegalus, found by Mr. Loat in the White Nile, x 2. 



w T ay pinnules, the rays of the dorsal fin of the very young are the same in number as in 

 the adult, but it is impossible to draw a limit between them and those of the caudal. 

 In the specimens obtained by Mr. Loat, the five anterior spines are not fully formed, 

 not bicuspid, whilst the others have already assumed their definite shape. The 

 median caudal rays are much elongate, the fin being acutely pointed *. 



In some of the larger species of Polypterus, such as P. bichir, P. lapradii, and 

 P. congicus 9 the external gills may persist late in life, specimens between 240 and 

 345 millimetres long being occasionally still provided with them. 



Hyrtl supposed the external gill of Polypterus to be homologous with the pseudo- 

 branch of Sturgeons. Budgett, who has made a study of the anatomy f , based on the 



* On the young of various species, cf. Boulenger, P. Z. S. 1902, i. p. 121, pis. x. & xi. 

 t Tr. Zool. Soc. xv. 1901, p. 323. 



