88 UNIVERSITY OF COLORADO STUDIES 



jaw short and included by the projecting lower jaw; angle of the mouth about 

 equidistant from the tip of the lower jaw and the anterior margin of the eye; pre- 

 maxillaries protractile; dorsal fin longer than high, inserted in the posterior half 

 of the body, slightly in front of the origin of the anal fin, the distance from the 

 base of the first ray of the dorsal to the base of the caudal reaching forward to the 

 posterior margm of the eye; dorsal rays 14 or 15, occasionally 16; pectorals not 

 reaching (females) or barely reaching (males) the ventrals; ventrals barely 

 reaching the anal fin; scales small, circular, circuli large and few, basal radii 8 to 

 12, apical radii none; lateral line wanting or represented by an occasional pore 

 only; scales 58 to 64 along the middle of the side, in 18-21 rows between the dorsal 

 and ventral fins; length under 6 inches. 



General color above greenish, shading from dark olive green to silvery white 

 below; sides yellowish to bright orange-yellow; a dark mid-dorsal spot just in 

 front of the dorsal fin; sides crossed by 11 to 21, usually 14 or 15, dusky vertical 

 bars which are generally narrower than the light interspaces, and in many indi- 

 viduals, particularly females, each alternate bar is lighter and narrower than two 

 adjacent to it; under parts of the head yellowish white; dorsal and caudal fins 

 more or less dusky; pectoral and ventral fins yellowish white; anal fin yellowish 

 to orange-yellow. The variation in the number of lateral bars is shown by the 

 following table, which includes the data from 11 1 specimens collected at one 

 station on the South Platte River at Julesburg, July 19, 191 2: 



Bars II 12 13 14 15 16 17 18 19 20 21 



Specimens i 6 16 23 26 15 12 8 2 i i 



Percentage 14 21 23 14 10 



In this series 82 per cent of the iii individuals had from 13 to 17 bars, the gamut 

 of variation being from 11 to 21 bars. 



This species, as the name Top-minnow implies, feeds to a considerable extent 

 upon surface insects, Entomostraca and floating matter. For such feeding the 

 upturned mouth is well adapted. On the other hand, the Zebra Fish is able to 

 take small snails, worms, insect larvae and diatoms, especially when placed under 

 conditions which limit the supply of surface food. The stomachs of specimens 

 collected at Julesburg in July from the South Platte River, then almost dry, were 

 filled with masses of diatoms, the sandy pools in which F. zebrinus had taken 

 refuge as the river receded containing at that time large quantities of brown 

 diatomaceous slime and few if any surface insects. The data concerning the 

 stomach contents of seventeen specimens are given below: 



South Platte River, Julesburg, July 19, 1912. Sandy pools. 

 70 mm., brown diatomaceous slime, 100 per cent. 

 50 mm., " " " , 75 per cent. Not full. 



65 mm., " " " , 95 per cent; Entomostraca 5 per cent. 



80 mm., " " " , 100 per cent. 



