From Boulenger (1903):
Petrocephalus ansorgii, sp. n. (Boulenger, 1903, illustrated Plate XXYIII. fig. 2.)
A single specimen from Agberi.
Depth of body 3 times in total length, length of head 4 and 1/3. Head slightly longer than deep; snout rounded, 1/6 length of head; mouth situated below the eye, its width 1/5 length of head; teeth bicuspid, 10 in the upper jaw, 20 in the lower; nostrils close together, close to the eye, a little above the level of its lower border; eye large, twice as long as the snout, 1 and 1/3 interorbital width. Dorsal 33, originating above 9th ray of anal, its length 1½ in its distance from head. Anal 39, equally distant from base of ventral and from base of caudal. Pectoral pointed, ¾ length of head, twice as long as ventral and extending beyond base of latter. Caudal with pointed lobes. Caudal peduncle 3 times as long as deep, 2/3 length of head. 45 scales in the lateral line, 11/13 in a transverse series on the body, 14/12 in a transverse series between dorsal and anal, 8 round caudal peduncle. Silvery, brownish on the back and on the anterior rays of the dorsal.
From Boulenger (1903): Total length 105 millim.
Holotype from Agberi, Lower Niger basin.
Distribution restricted to the Lower Niger basin.