132 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Body deep, compressed ; dorsal contour arched, its highest point at insertion of dorsal ; caudal 
peduncle narrow and very deep; head small, pointed; interorbital space wide, slightly convex; eye 
large, a little nearer tip of snout than to posterior edge of opercle; mouth vertical. Teeth in two 
series ; the hrst in a single row, minute, flat, and pointed, the second in a villiform hand, much smaller 
and narrower than first, brownish colored, strongly curved backward. Gill-opening extending above 
base of pectoral a distance equal to diameter of pupil. Gillrakers on first arch 19, slender, the length 
of longest equal to half diameter of eye. Intestinal canal slender and long. Peritoneum black. 
Scales on head and body large. One large, round scale on interorbital space, followed by 2; a 
row of 11 from the latter to first dorsal ray; 3 rows of scales on base of caudal lin. 
Base of dorsal fin short, 4.16 in body; first ray shortest, the others graduated to the eighth, 
which is longest; the ninth, tenth, and eleventh shorter; twelfth and thirteenth longer; the abrupt 
shortening of ninth, tenth, and eleventh rays makes a notch in outline of dorsal. Anal advanced, its 
origin under third ray of dorsal; first ray greatly enlarged and lengthened, second and third equally 
lengthened, but more slender; these three with their connecting membranes form a half tube, with a 
pointed end ; other rays half the length of first. Upper lobe of caudal rounded ; 5 lower rays forming 
a very long, blunt appendage. Yentrals pointed, extending almost to tip of anal. Pectorals sharply 
rounded. 
Color yellowish-olive, marked with black. During life there were 4 narrow longitudinal orange 
bands, each extending along a row of scales on body. Top of head and a median dorsal band 
extending to caudal, dusky; a narrow dusky band on edge of lower jaw; 2 short vertical bands on 
snout; 6 upper rows of scales edged with black, or dusky; a few black spots irregularly arranged on 
body above ventrals; a large black spot at base of caudal, its color extending along upper edge of 
prolongation ; a dark line extending along lower edge of caudal peduncle to end of lower caudal rays; 
the caudal extension with a light central portion bordered with black; the lower border wider; under 
part of head and belly without dark color; dorsal fin with black dots and lines; pectorals, ventrals, 
and anals plain. 
Considerable variation in shapes of lins and in color is shown among other male specimens. In 
some the fins are low or short, the caudal ornament represented only by a slight lengthening of lower 
rays. Among individuals, apparently fully grown, there is every gradation from the undeveloped to 
the very long caudal extension. In every case the scales are conspicuously dark-edged. In some 
examples black spots crowded together form a more or less definite dark line from eye to caudal, while 
below this line are large, irregular, black blotches. Others have no black spots, and the dark caudal 
patch lias almost disappeared. 
The females have the fins low or short, and without special modifications; the posterior edge of 
caudal, with the upper part rounded, the lower pointed. Scales dark-edged, a narrow, indefinite, 
dark, color-hand usually present along median line of sides; the dark caudal patch is rarely absent. 
Fully grown males are scarce, a large catch consisting mostly of females and young. 
Xiphophorus montezumce is distinguished from other known species of the genus by having 7 anal 
rays, the scales with conspicuous dark edges, a large caudal spot, and the caudal appendage not 
sword-shaped, but with its end enlarged and blunt. 
