Diagnosis: last simple dorsal-fin ray forming ossified spine longer than head in specimens over 150 mm SL. B. bynni occidentalis: scale formula 5.5/26-31/4.5-5.5; 2.5-3 scales between lateral line and middle of belly, behind pelvic-fin origin; 12 scales around caudal peduncle; dorsal fin with 4 unbrached and 9 branched rays; anal fin with 3 unbranched and 5 branched rays; pectoral fin with 16-19 rays; pelvic fin with 1 unbranched and 8 branched rays; 3-5/12-15 gill rakers on first gill arch (Ref. 2940, 81282). B. bynni waldroni: scale formula 4.5/24-28/4.5; 2.5 scales between lateral line and middle of belly, behind pelvic-fin origin; 12 scales around caudal peduncle; dorsal fin with 4 unbranched and 9-10 branched rays; anal fin with 3 unbranched and 5 branched rays; pectoral fin with 1 unbranched and 14-16 soft rays; pelvic fin with 1 unbranched and 8 branched rays; 3-6/14-17 gill rakers on first gill arch (Ref. 2940, 81282).

Description: large species, body rather deep in adults and slightly compressed; lips well developed, forming rounded mental disk; lips may be hypertrophic ("rubber-lip") in some individuals of B. bynni waldroni; last simple dorsal-fin ray forms thick spine in adults; spine grows, being shorter than head in juveniles and longer than head in specimes over 150 mm SL; longest dorsal-fin ray is first branched ray; distal margin of dorsal fin slightly concave (Ref. 2940, 81282).

Coloration: B. bynni occidentalis: in life: sides yellowish tinged with orange, back greyish; fins more or less bright yellow except for caudal fin, which is orange in juveniles and medium-sized adults, and greyish in older fish; distal margins of dorsal and caudal fins black-edged (Ref. 2940, 81282). Preserved specimens: brownish (Ref. 2940, 81282). B. bynni waldroni: ground color yellowish to greenish; fins colourless; dorsal and caudal sometimes tinged with red-violet-pink (Ref. 2940, 81282).