from Boulenger 1909, pp. 67-68:
Depth of body 19 to 23% of total length, length of head 15 to 22%. Head depth 80 to 83% head length; snout convex, 25 to 28.5% length of head, slightly projecting beyond mouth; mouth small, subinferior, its width 20% length of head; teeth small, feebly notched, 5 in upper jaw, 6 in lower; nostrils nearly equally distant from end of snout and from eye, anterior on a level with centre of latter, posteiior with lower border; eye small, about ½ length of snout or interorbital width. Dorsal 15-18, hardly 1/3 as long as its distance from head, originating above 10th to 14th ray of anal. Anal 25-30, nearly 2 to 2½ times as long as dorsal, nearer base of caudal than base of ventral. Pectoral obtusely pointed, at least 3/4 length of head, 1½ to 1 2/3 length of ventral, reaching base of latter. Caudal densely scaled in the basal half, with pointed lobes. Caudal peduncle 2½ to 3 times as long as deep, as long as head or a little shorter. 58-64 scales in lateral line, 8-10 / 13-14 in transverse series on body, 7-9 / 6-7 in transverse series between dorsal and anal, 12 round caudal peduncle. Brown.
to 175 mm SL.
Molecular phylogenetic studies (Sullivan et al. 2000; Lavoué et al. 2003) place Brienomyrus brachyistius (with, presumably, its congener B. longianalis) as the sistergroup to Isichthys henryi. These together are the sistergroup to all mormyrins exclusive of the genera Mormyrops and Myomyrus.
Brienomyrus brachyistius is found in the rivers of coastal West Africa and Lower Guinea, including the Ogooué River of Gabon, though absent from the upper Ivindo River, an Ogooué tributary.