. Bulletin of the British Museum (Natural History) Zoology. REDESCRIPTION OF TILAPIA GUINASANA 25 M = in the four largest fishes]. Cheek depth showing positive allometry with standard length, (M = )% of head length [, M = in the four largest fishes]. Lower jaw (M = )% of head length, and from as long as it is broad to times longer than broad (modal range times longer). Mouth sloping slightly upwards; lips moderately thickened. Maxilla with a variable posterior extent, closely approaching a vertical through the anterior orbital margin
. Bulletin of the British Museum (Natural History) Zoology. REDESCRIPTION OF TILAPIA GUINASANA 25 M = in the four largest fishes]. Cheek depth showing positive allometry with standard length, (M = )% of head length [, M = in the four largest fishes]. Lower jaw (M = )% of head length, and from as long as it is broad to times longer than broad (modal range times longer). Mouth sloping slightly upwards; lips moderately thickened. Maxilla with a variable posterior extent, closely approaching a vertical through the anterior orbital margin in one specimen, but in the others reaching either a point midway between the nostril and the orbit or slightly beyond that point. Caudal peduncle length (M = )% of stan- dard length, its length-depth relationships variable, the majority of specimens with the peduncle deeper than it is long (its length 80-90% of its depth) the others with the peduncle slightly longer than deep ( times). No correlation was found between this ratio and specimen size or coloration. Gill-rakers. 8-11 (rare), mode 10, in the outer row on the ceratobranchial of the first arch. The rakers are short and stout (the anterior one or two shorter than the succeeding ones) and have a characteristic pyramidal shape (Fig. 2) quite unlike the narrow-based, flattened, triangular and more elongate rakers in T. sparrmanii. Microbranchiospines are present on the outer faces of gill-arches 2 to 4. Scales. On all parts of the body the scales are cycloid and have a very characteristic rugose appearance over their entire exposed surfaces, but especially over the central region in scales on the cheeks and flanks. When compared with the scales of T. sparrmanii, those of T. guinasana are thicker and denser. There are 25(f5), 26(fl2), 27(f4) or 28(fl), mode 26, scales in the lateral series. In one specimen no scales in the upper lateral-line are pored, but in the others ll(fl), 12(f2), 13(f3), 14(f4),
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