40 MOKMYBIDJE. 



3. MARCUSENIUS. 



Gill, Proc. Ac. Philad. 1862, p. 129 ; Boulenger, Proc. Zool. Soc. 1898, p. 792, and Poiss. Bass. 



Congo, p. 74 (1901). 

 Heteromormyrus, Steindachner, Verh. zool.-bot. Ges. Wien, xvi. 1866, p. 765. 



Teeth in the jaws small, truncate or notched (3 to 9 in the upper jaw, 4 to 10 in 

 the lower); minute conical teeth on the parasphenoid and on the tongue; mouth 

 inferior or subinferior, below the level of the eyes. Nostrils widely separated. Body 

 short or moderately elongate ; ventral fins midway between pectorals and anal, or 

 nearer the former. Dorsal and anal fins subequal in length, or either the one or 

 the other the longer. Vertebrae 37-46 (9-12 + 4-5 + 23-30). 



Twenty-three species are known, four of which are represented in the Nile system. 



Synopsis of the Species. 



I. 16 to 20 scales round caudal peduncle; anal originating in advance of dorsal; posterior nostril 



close to the eye. 



Dorsal 15-18 ; anal 23-25 ; lateral line 46-53 ; caudal peduncle two- 

 thirds to three-fourths length of head . I. M. nigricans, Blgr. 



Dorsal 18-22 ; anal 22-26 ; lateral line 53-60 ; caudal peduncle four- 

 fifths to once length of head 2. M. iddori, O. & V. 



II. 12 scales round caudal peduncle ; posterior nostril remote from the eye. 

 Dorsal 31, anal 31, both fins originating in the same vertical ; lateral 



line 87 3. Af. liarringtoni, Blgr 



Dorsal 34-36 ; anal 24-26 ; dorsal originating far in advance of anal ; 



lateral line 55-65 . 4. M. petherid, Blgr. 



1. MAECUSENIUS NIGRICANS. 

 (Plate IX. fig. 2.) 

 Boulenger, Ann. & Mag. N. H. (7) xvii. 1906, p. 434. 



Body strongly compressed, its depth three to three and a half times in the total 

 length; length of head four to four and one-third times in the total length. 

 Head as long as deep, not quite twice as long as broad ; snout about one-fifth 

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

 below the nostrils, its width about four 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 a little lower down, close to the eye ; eye moderate, as long as the snout, one-half 



