114 FISHES OF ILLINOIS 



Genus HYBOGNATHUS Agassiz 



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

 lower in some species with a slight hard protuberance in front; premaxil- 

 laries protractile; no barbel; teeth 4-4, with oblique grinding surface and 

 little if any hook; alimentary canal 3 to 10 times length of body; peri- 

 toneum black; dorsal rays 8 ; anal rays 7 to 9 ; scales large, usually 32 to 41 

 in lateral series; lateral line complete. Size moderate, 2\ to 6 inches. 

 •Described species numerous, though most are imperfectly known, and 

 doubtless many synonyms. Central 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 hard protuberance at tip of inside of lower 



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



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



no symphysial protuberance; teeth short and distinctly hooked; length 



2^ inches nubila, 



HYBOGNATHUS NUCHALIS Agassiz 

 (silvery minnow) 



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

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

 (also argyritis); F., 79; F. F., I. 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.S 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 life; sides clear 

 silvery, with bright reflections; fins unspotted; scales not distinctly dark- 

 edged, their entire surface being about equally specked. Head small, 

 slender, subconical, its length 4 to 4.6, its width 1.8 to 2.1 in its length; in- 

 terorbital space gently convex, 2.S to 2.9 in head; eye small, circular, 3.8 

 to 4.S 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 falling far short of 

 orbit, scarcely exceeding as a rule the vertical from anterior nostril-open- 

 ing; lower jaw with a hard sharp edge and a noticeable protuberance just 

 inside the mouth at the symphysis of the mandibles; jaws about equal; 

 isthmus less than pupil. Teeth 4-4, narrow, with little grinding surface 

 and very little hook; intestine extremely variable in length, from 3.7 to 8 

 times length of head and bodv, being as a rule over S ; peritoneum dusky. 



