114 FISHES OF ILLINOIS 



consists, in all the cases examined by us, mainh' of mud con- 

 taining algse with an occasional trace of Entomostraca. 



The breeding season falls in May and June, at which time 

 the colors of the male reach their most gorgeous development. 

 While not especially hardy, this species lives well in the aqua- 

 riimi, where it is indeed a most beautiful object. 



Genus HYBOGNATHUS Agassiz 



Body elongate, somewhat compressed; jaws normal, sharp-edged, the 

 lower in some species with a slight hard protuberance in front; premaxillaries 

 protractile; no barbel; teeth 4—4, with oblique grinding surface and little if 

 any hook; ahmentary canal 3 to 10 times length of body; peritoneum black; 

 dorsal rays 8; anal rays 7 to 9, scales large, usually 32 to 41 in lateral series; 

 lateral hne complete. Size moderate, 2}4 to 6 inches. Described species 

 numerous, though most are imperfectly known, and doubtless many syn- 

 onyms. Ventral and southwestern United States into northern Mexico; 

 two species found in Illinois. 



Key to the Species of HYBOGNATHUS found in Illinois 



a. Silvery species, with a prominent liard protuberance at tip of inside of lower 



jaw and "with teeth long and scarcely hooked; length 6 inches nuchalis. 



aa. Olivaceous, with dark lateral band continued through eye to end of snout; 

 no symphysial protuberance; teeth short and distinctly hooked; length 

 21/^ inches nubila. 



HYBOGNATHUS NUCHALIS Agassiz 



silvery minnow 



(Map XXV) 



Agassiz, 1855, Am Jour. Sci. Arts (Silliman's Journal), XIX, 224. 



G., VII, 184; J. & G., 156; M. V., 53; J. & E., I, 213; N., 45 (also argyritis). J., 56 

 (also argyritis); F., 79; F. F,, L 6, 79; L., 14. 



A large silvery minnow, with large and loosely imbricated scales, spindle- 

 shaped body and pointed head, the lower jaw thin and hard and furnished 

 with a small hard lump just inside the mouth in front. Length 6 inches, 

 body subfusiform, not much compressed, deepest at front of dorsal and 

 tapering about equally backward to base of caudal and forward to the pointed 

 snout; depth 3.9 to 4.5 in length; caudal peduncle rather stout, shorter than 

 head, its depth 1.7 to 2.3 (usually less than 2) in its length. Color olivaceous 

 green above, translucent in hfe; sides clear silvery, \\dth bright reflections; 

 fins unspotted; scales not distinctly dark-edged, their entire surface being 

 about equally specked. Head small, slender, subcorneal, its length 4 to 4.6, 

 its width 1.8 to 2.1 in its length; interorbital space gently convex, 2.5 to 2.9 

 in head; eye small, circular, 3.8 to 4.5 in head; nose 2.9 to 3.5 in head, pointed 

 and considerably longer than the small eye; mouth small, terminal, oblique, 

 tip of upper lip not far below level of middle of pupil; maxillary 3.6 to 4.3 in 

 head, its length but little greater than diameter of eye; back of maxillary 



