42 MORMYBIDJE. 



Seventeen specimens, measuring from 80 to 93 millimetres, were obtained by 

 Mr. E. Degen at the mouth of the Katonga River, at the north-west of Lake Victoria, 

 on Nov. 5, 1905. 



This species is very closely allied to M. isidori, but diifers in the shorter dorsal fin, 

 the shorter caudal peduncle, the larger mouth, and generally fewer scales in the 

 lateral line. 



2. MARCUSENIUS ISIDORI. 

 (Plate VII. fig. 1.) 



Mormyrus isidori, Cuvier & Valenciennes, Hist. Poiss. xix. p. 285 (1846) ; Giinther, Cat. Fish. vi. 



p. 221 (1866), and Petherick's Trav. ii. p. 256 (1869). 

 Petrocephalus isidori, Marcusen, Bull. Ac. St. Petersb. xii. 1851, p. 14, and Mem. Ac. St. Petersb. 



(7) vii. 1864, no. 4, p. 150, pi. v. fig. 20. 

 Marcusenius isidori, Boulenger, Proc. Zool. Soc. 1898, p. 798. 



Body strongly compressed, its depth twice and three-fourths to three and one -third 

 times in the total length ; length of head four to four and a half times in the total length. 

 Head as long as deep, nearly twice as long as broad ; snout one-fifth to one-fourth 

 the length of the head, rounded, projecting beyond the mouth ; mouth situated below 

 the nostrils, its width four and a half to five times in the length of the head ; teeth 

 small, bicuspid, 7 in the upper jaw, 8 in the lower ; anterior nostril on a line with the 

 centre of the eye, midway between the latter and the end of the snout ; posterior 

 nostril close to the eye, near its lower border ; eye moderate, as long as the snout, one- 

 half to three-fifths the interocular width. Dorsal fin with 18 to 22 rays, originating 

 above third or fourth ray of anal, its length about half its distance from the head ; 

 anterior rays longest, forming a point. Anal fin with 22 to 26 rays, nearly equally 

 distant from the base of the ventral and from that of the caudal ; the fin more pointed 

 in front in females than in males. Pectoral fin pointed, subfalcate, as long as or a 

 little shorter than the head, twice to twice and a half as long as the ventral, and 

 extending beyond the root of the latter. Cauda] fin scaled at the base, with pointed 

 lobes. Caudal peduncle twice and a half to three times as long as deep, as long as 

 or a little shorter than the head. 53 to 60 scales in the lateral line, T ^ =l7 in a 

 transverse series on the body, j^j| in a transverse series between dorsal and anal, 

 16 or 18 round caudal peduncle. 



As preserved in spirit, this little Mormyr is brown on the back and silvery white 

 beneath, uniform or dotted with brown. A living specimen sent by Capt. Flower to 

 Capt. Vipan was of a purplish grey above, strongly iridescent, the fins colourless and 

 transparent. 



100 millimetres appears to be the greatest length reached by this species. 



