66 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Potomac Biver are concerned, seems to apply only to tlie females, while tlie males 
have a similar number of brilliant silvery crossbars on an olivaceous background. 
This conclusion is borne out by the examination of 71 adult males and 54 egg-bearing 
females. 
The following description of the sexes, based on Potomac specimens, is offered : 
Male . — Form elongated, slender. Head depressed, of moderate length. Dorsal 
fin low, beginning considerably in advance of anal and nearer base of caudal than 
snout. Anal short, deeper than dorsal. Ventrals about equal to portion of head 
posterior . to eye, not reaching vent. Body uniformly olivaceous, darkest above, with 
about 20 silvery vertical bars, rather narrower than the interspaces, which are the 
color of the body. . Dorsal usually plain, occasionally faintly mottled with black and 
white spots. Other fins plain. Mouth nearly horizontal, width of eye, on level with 
pupil, lower jaw projecting, angle of jaw half-way between eye and end of lower jaw. 
A dark purplish spot on opercle opposite eye. 
Female . — Similar to male in form and size. The body marked by 15 to 20 dark 
transverse bars, much narrower and shorter than the silvery bars in the male, the 
interspaces lighter than in the male. Back sometimes spotted. Oviduct sheathing 
the anterior part of anal. Ventrals not reaching vent. 
Eye large, 3£ in head, 1J in interorbital space, and 1£ in snout; head, 34; depth, 4£. 
Dorsal, 13; anal, 11. Scales, about 45-15. Length, 3.J or 4 inches. 
Prof. Jordan, in his “Beport of Explorations in the Alleghany Begion of Virginia, 
North Carolina, and Tennessee,”* etc., records the capture at Luray, Virginia, in the 
Shenandoah Biver, of a specimen of Fundulus diaphanus u with about 15 silvery cross- 
band.s, most of them narrower than the dark interspaces; back and fins unspotted.” 
That form of F. diaphanus formerly called menona is saidt to occasionally have silvery 
crossbars instead of black ones. These are the only references to silvery transverse 
bars met with in the descriptions of this species. 
All immature specimens are distinctly marked by dark vertical bars, on a pale 
olivaceous background. When the fish reaches the length of about 2 inches, the 
differential sexual characters, as before defined, begin to be manifested. A series of 
102 young specimens was preserved, the smallest being seven-eighths of an inch long. 
5. Fundulus heteroclitus (L.). Common TcUlifish; Mud dabbler. (PI. xix.) 
Next to F. diaphanus this is the most abundant killifish in the region. 120 speci- 
mens were preserved, of which 81 were adult and 39 were immature individuals. 
This species is subject to considerable variation in color, depending on sex and 
age. The complete series of specimens obtained has permitted a satisfactory diagnosis 
of even the smallest examples. 
Among 36 adult males, the largest specimen is 44 inches long. As the male 
approaches maturity the distinct dorsal ocellus, which is more or less constant in the 
young, usually disappears, and it is rarely seen in adults, although in a few specimens 
the vestiges remain in the form of a dark spot on the already dark or mottled fin; the 
ocellus is rarely found in examples over 24 inches long. In some adults the white 
spots on the body, instead of being disposed in narrow vertical stripes and irregularly 
scattered over the sides, as usually described, are found on the anterior part of each 
Bulletin U. S, Fish Commission, vm, 1888, p. 103. 
t Manual of the Vertebrates. 
