146 FISHES OF ILLINOIS 



the great uniformity in size of the scales; a rather broad but faint verte- 

 bral streak; two black blotches on the posterior membranes of the dorsal 

 (fainter in females) ; paired fins, lower part of belly, tips of anal and cau- 

 dal, and the front and upper margin of the dorsal charged with clear 

 satin -white pigment in males in the spring; basal half of dorsal in full 

 breeding dress light green; lower fins lemon-yellow, except tips of ventrals 

 and anal. Head small, subconic, not so stout as in the last species, 3 .9 to 4. 2 

 in length ; profile scarcely angled at nape; width of head 1 . 9 to 2 . 2 ; inter- 

 orbital space 2.5 to 2.7 in head, ver\^ convex; eye small, 3.9 to 4.8 in 

 head; nose somewhat longer than in the last species, 2 .8 to 3 .2 in head, 

 conic and usually more or less upturned, especially in males; mouth 

 slightly less oblique than in the last, the tip of the upper lip scarcely above 

 level of lower margin of orbit; maxillary longer than eye, reaching to 

 back of posterior nostril-opening, but not to orbit, 3.1 to 3.6 in head; 

 lower jaw shorter than upper; isthmus less than pupil. Teeth usually 

 1, 4-4, 1*, the edges of the grinding surface often more or less crenate, 

 intestine .8 to .9 times length of head and body; peritoneum silvery, 

 finely specked with black. Dorsal fin with 8 rays, set a little behind the 

 ventrals, its longest ray usually a little less than head, in which it is con- 

 tained 1 . 9 to 1.2; anal rays 8 or 9 ; pectorals 1.2 to 1 . 4 in head, about | 

 to ventrals in fully grown specimens, ' about | in young but sexually 

 mature males; ventrals to vent in females, past front of anal in males. 

 Scales 6, 36-39, 3 ; 14 to 16 before dorsal, where they are scarcely crowded; 

 lateral line decun,^ed anteriorly to about parallel with lower outline. 



Extremely abundant in Illinois, especially in the smaller streams 

 of the central part of the state, and taken in 270 of our collections. 

 A species of the creeks and smaller rivers in this state, its frequency 

 ratios for those streams being approximately 2^, while those for 

 lakes and the larger rivers are but .11 and .35 respectively. It 

 shows a marked preference for swift water and for a clean bottom, 

 our coefficients for these situations being 1.3 and 1.6 respectively. 

 It is generally distributed from Lake Champlain and the St. Law- 

 rence River through the lakes of central New York and the Great 

 Lake basin to Minnesota, Pennsylvania, Virginia, northern Ala- 

 bama, and Arkansas. 



Two thirds of the entire food of 33 specimens examined, con- 

 sisted of insects, nearly half of which were terrestrial. Three of 

 our specimens had eaten small fishes, and a mixture of vegetable 

 elements derived from both aquatic and terrestrial plants had been 

 eaten mainly by four, one of which had fed only on algae, while 

 three others had taken some 90 per cent, of their food from miscel- 



*Cases of apparent N. whipplii in which the teeth are 4-4 or 1, 4-4, 1 occur 

 in a few collections from locaHties in which A'^. lutrensis and N . whipplii seem to 

 intergrade. In general our collections show, however, that little variation need 

 be looked for in this species. 



