Diagnosis: While no ambiguous morphological autapomorphies have been located to diagnose Phenacogrammus concolor, the species is nonetheless distinguished from all congeners except P. deheyni and P. flexus in the possession of a prominent anterior expansion of the first pleural rib; it is readily differentiated from both in the absence of a dominant pigmentation patterning over the flanks and caudal peduncle; additionally, it differs from P. flexus in a shallower body depth, 24.9% of standard length vs. 27.0%, and in the possession of 7 supraneurals vs. 6 (Ref. 127185).

Description: A small-bodied species; body elongate, laterally compressed with greatest body depth, 24.9% of standard length, well in front of dorsal-fin origin, in front of the level of pelvic-fin insertion; dorsal body profile smoothly convex to dorsal fin, slightly less so to caudal-fin base; ventral profile smoothly convex between isthmus and anal-fin base, caudal peduncle longer than deep (Ref. 127185). Head length short, 21.7% of standard length, eye large, bony orbit diameter 44.8% of head length (Ref. 127185). Mouth terminal, lower jaw prominent and slightly prognathous, lower lip thick; premaxilla with two teeth in outer row, each bearing 3 cusps, positioned opposite interspaces between and alternating with 4 inner row teeth bearing 5-6 cusps; four robust, broad-based, outer-row teeth on each dentary, first 3 bearing 5-6 cusps, and 4th greatly reduced in size bearing 3 cusps; two small, conical, symphyseal teeth located immediately behind outer row series on dentary (Ref. 127185). Dorsal-fin rays ii,7-8, fin possitioned midway between snout and caudal-fin base, with origin at, or slightly in front of, pelvic-fin insertion, first two branched rays not elongated; anal fin iii,15-16 rays, no hypertrophy or posterior curvature of anal fin in males; caudal fin forked, with 9 upper and 9 lower principal rays, no median filamentous extension (Ref. 127185). Scales in longitudinal series 26-28 to caudal flexure, 3 or 4 transverse scales between longitudinal series and dorsal-fin origin, 3 transverse scales between longitudinal series and pelvic- fin insertion; pored scales in truncate lateral line 5-7; circumpeduncular scales 10 (Ref. 127185). Vertebral count 31-33; twelve to 13 pleural ribs, first with prominent rounded expansion on anterior face in upper third; seven tubular supraneurals located between interspaces of neural spines of vertebral centra 4-11 (Ref. 127185).

Colouration: In preservation, base body colouration greyish brown, darker dorsally and becoming pale yellow on chest and ventrum; an overlay of bluish iridescence covers most of body; snout and dorsum of head dark brownish black, cheek silver with a few scattered melanophores; a large humeral blotch present at midbody, above pectoral fin; other than humeral blotch no prominent pigmentation along flanks or caudal peduncle; dorsal and adipose fin light grey, anal fin dusky distally, pectoral and pelvic fins hyaline with darkly pigmented leading edges; median rays of caudal fin somewhat darker than above and below (Ref. 127185). Colouration and pigmentation shortly postmortem like that in preservation, but more intense (Ref. 127185).