GILBERT: FISHES OF THE SUBGENUS LUXILUS


 Three well-defined species groups are recognizable within the
subgenus: The coccogenis group contains two species (N. coccogenis
and N. zonistius), as does the zonatus group (N. zonatus and N. pils-
bryi); the cornutus group consists of five forms (N. cornutus, N. albe-
olus, N. chrysocephalus chrysocephalus, N. chrysocephalus isolepis,
and N. cerasinus). The first two species pairs are completely allo-
patric, but cornutus and its immediate relatives exhibit variable geo-
graphic relationships.
 The coccogenis group is defined as follows: body strongly com-
pressed or not; peritoneum heavily speckled with black pigment but
never uniformly black; dorsal fin inserted slightly behind pelvic; scales
along anterior-lateral part of body somewhat taller than wide; poste-
rior borders of scales along side of body smooth and without scallops;
nuptial tubercles weakly developed, nearly granular in some areas;
tubercles present in two or three rows along lower jaw, present on
tip of chin, on upper part of head concentrated mainly along side
and tip of snout; tubercles either present or absent on top of head or
back; tubercles present in both sexes, though poorly developed in
females; crescentic vertical streaks moderately developed, not evi-
dent in some individuals; a red bar present on cheek or on margin of
opercle and preopercle; caudal spot present or absent; a consistent
pattern of dark pigmentation in the dorsal fin, either present or absent
in the caudal fin; circumferential scales usually 13 to 16-2-10 to 12;
caudal peduncle scales normally 7-2-5 or 6; no black lateral stripe
on side of body.
 The zonatus group has the following characters: body terete, not
strongly compressed; peritoneum uniformly black; dorsal fin inserted
slightly behind pelvic; scales along anterior-lateral part of body only
slightly taller than wide; posterior edge of scales along side of body
each with four or five definite scallops; nuptial tubercles weakly de-
veloped; tubercles granular, present in a single row along lower jaw,
absent from tip of chin, present on top of head; tubercles pres-
ent in both sexes, though weakly developed in females; crescentic
vertical streaks absent from side of body; no red bar present on cheek
or on margin of opercle and preopercle; caudal spot absent; no per-
sistent pattern of dark pigmentation in either dorsal or caudal fin;
circumferential scales usually 12 or 13-2-12 or 13; caudal peduncle
scales normally 7-2-5 or 6; a distinct black lateral band present along
side of body and encircling snout; a narrow, short secondary stripe
running parallel and slightly dorsad to main lateral band.
 The cornutus group may be diagnosed as follows: body deep and
 compressed, this character being quite variable among different popu-


1964