Description of Marcusenius retrodorsalis from Nichols & Griscom 1917:
Close to M. sphecodes, but eye smaller, 4 times in interorbital; dorsal and anal placed much further back, so that dorsal origin is equidistant from tip of pectoral and base of caudal; caudal peduncle 2 1/2 times as long as deep; teeth 7/8.
The type, our only specimen, No. 6933, American Museum of Natural History, Niapu, Congo, Nov. 1913, from a small forest brook tributary to Bima River, measures 114 mm. in length to base of caudal; depth of body equal to length of head, 5 times in this measure. Head slightly longer than deep; snout rounded, 3 3/4 times length of head; mouth small, subinferior, its width 1/5 length of head; teeth small, notched, 7 in upper jaw, 8 in lower; nostrils midway between eye and end of snout, the posterior on a line with lower border of eye; eye very small, 1/3 length of snout, 1/4 interorbital width. Dorsal 17 originating above 5th ray of anal, not 1/2 as long as its distance from head, it origin equidistant from tip of pectoral and root of caudal. Anal 24, much nearer root of caudal than base of ventral, about 1 1/3 as long as dorsal. Pectoral pointed, 3/4 length of head, 1 1/2 length of ventral, not reaching base of latter. Caudal with pointed lobes. Caudal peduncle 2 1/2 times as long as deep. 67 scales in lateral line, 12 around peduncle. Uniform brown.