■go UNIVERSITY OF COLORADO STITDIES 



the length of the body; eye large and prominent, situated a little nearer the tip 

 of the snout than to the posterior margin of the operculum, rather high on the side 

 of the head; dorsal margin of the eye on a level with or slightly above the flat 

 portion of the top of the head; diameter of the eye 3 . 5 to 4 in the head, i . 5 to 

 2 in the interorbital distance, and i to i . 2 in the snout; nostrils very small, dorsal, 

 on a level with the anterior margin of the eye; mouth terminal and horizontal; 

 upper jaw small, included by the large, projecting lower jaw; premaxillaries 

 protractile; angle of the mouth about midway between the tip of the lower jaw 

 and the center of the eye; dorsal fin small, low, its longest ray being almost equal 

 to the base of the fin in length, inserted well back in the posterior half of the body; 

 base of the first ray of the dorsal almost on a level with the first ray of the anal 

 fin (females) or distinctly posterior to the first ray of the anal (males) ; dorsal rays 

 usually 10, often 9 or 11 ; pectorals small, not reaching the ventrals; ventrals very 

 small, just reaching the anal opening (females) or the first anal rays (males); 

 anal fin as large (females) or larger than (males) the dorsal fin; anal rays 12 or 

 13; caudal fin large, fan-shaped and not forked, its greatest width equal to or 

 slightly less than that of the body; scales rather large, 28 to 33 along the middle 

 of the side, 10 to 12 rows from the dorsal fin to the ventral; lateral line wanting; 

 scales roughly circular, circuli large, basal radii 10 to 15. 



General color greenish gray to olivaceous, darker dorsally, shading into white 

 or cream color below and having a narrow but distinct dark mid-dorsal band; 

 fins hyaline, dorsal greenish; pectorals, ventrals and especially the anal yellow, 

 broadly edged with cherry-red to crimson; scales outlined with yellowish brown. 



This little fish is a true top-minnow and may often be observed swimming just 

 under the surface. Individuals kept in an aquarium at the University were found 

 to spend most of the time at the surface with the tip of the snout just breaking the 

 surface film. In this position they remained absolutely quiet for many minutes 

 at a time or moved slowly back and forth across the tank. There was no evidence 

 that this species swims in pairs as the name Zygonectes implies. The position of 

 the fish at the surface was the same in light and dark, as they were always found 

 at the surface late in the night as well as in the middle of the day. When dis- 

 turbed or at night when the room was suddeiJy illuminated they immediately 

 darted to the bottom, resting on the floor of the tank in the more shaded portions. 



The data concerning the stomach contents of twelve specimens of this species 

 show both surface forms and bottom forms to be included in the food of 

 F. fioripinnis. 



South Platte River, Julesburg, July 19, 1912. 



50 mm., four gastropods, largest 4 mm., Physa sp., 100 per cent. (Probably the young of 



Physa Jorsheyi Lea, det. J. Henderson.) 

 45 mm., nine caddis-fly larvae, 75 per cent; two large adult muscid diptera, one being a 



housefly; three cladocerans. 

 55 mm., caddis-fly larvae, 100 per cent. 



