1902.] YOUNG OF POLYPTERUS. 123 



young, differ so greatly in shape, their numbers are the same 

 as in the adult, and, though devoid of spines and in no- way 

 " pinnules," the rays of the dorsal fin are identical in number ; 

 only, as it is practically impossible to establish a limit between 

 them and those of the caudal, it is preferable to count the rays 

 right to the extremity of the vertebral column. 



PoLYPTERUS LAPRADii Stdr. (Plate X. figs. 1 & 2.) 



This is one of the largest species, growing to a length of 

 740 millim. The largest specimen with fully developed opercular 

 gills, obtained by the late P. Delhez at Kaedi, Senegal, measures 

 300 millim., and is the largest Polypterus with external gills yet 

 recorded ; the specimens in which the external gills were discovered 

 by Steindachner measured up to 230 millim. These gills are 

 retained, as a rule, until the young is 240 to 260 millim. in 

 length, but they vary in the degree of development irrespective 

 of the size of the specimen, and sometimes also on the two sides. 



Four young specimens, measuring 94, 98, 114, and 205 millim. 

 respectively, were obtained at Assay and Abo, Southern Nigeria, 

 in October last by Dr. W. J. Ansorge, to whom ichthyology is 

 indebted for so many striking discoveries in that part of Africa. 



In the smallest specimen the external gill measures 30 millim., 

 the dorsal rays are all simple and spineless, 23 in number, and the 

 scales are very thin, circular, juxtaposed, and only well developed 

 about the lateral line and on the tail ; the caudal fin is acutely 

 pointed, the median rays being produced and as long as the head. 

 A black band extends on each side from the end of the snout, 

 through the eye, to the base of the external gill, which is likewise 

 black, and along the body to the base of the caudal fin ; this band, 

 on the body, is about as broad as the eye ; below it a narrower 

 black band extends from the shoulder to the anal fin. In the 

 two next specimens the external gills measure 33 and 50 millim. 

 respectively. In the largest specimen, the right external gill 

 measures 68 millim., the left 53 ; the scales are well developed, 

 rhomboidal and imbricate, and the dorsal spines (14 in number, 

 followed by 10 soft rays to the extremity of the vertebral column) 

 are ossified and bicuspid, supporting three articulated rays to 

 form the "pinnule." Tlie dark bands are more indistinct and 

 crossed by bars on the caudal region. 



Polypterus congicus Blgr. (Plate XI. fig. 1.) 



This species appears to be the largest of the genus, growing to 

 one metre. I have already reported upon specimens up to 260 

 millim. provided with the external gill, and one of them has 

 been figured in the ' Annales du Musee du Congo.' It appears 

 that in this species, as in P. Icqjradii, the external gills are 

 normally retained until comparatively late. A specimen recently 

 received from Banzyville on the Ubangi, and belonging to the 

 Congo Museum, is interesting as being the smallest yet obtained 

 of that species. > 



