HADROPTERUS — BLACK-SIDED DARTERS 283 



seventy collections of the species, being 2.26 and 1.6 respectively. 

 In the larger rivers, on the other hand, and in lakes, ponds, and 

 sloughs, it is much less common, its ratio for each being .58. 

 It is decidedly more frequent in northern Illinois than in either 

 central or southern. It is not particularly choice of localities, 

 and enters freely the turbid waters of the lower Illinoisan 

 glaciation. It has been taken several times along the banks of 

 the Illinois River, and from bays and bottom-land lakes con- 

 nected with that stream. It is not a swift-water species, and 

 has but little in its habits, food, or favorite situations, to identify 

 it with the darters at large. 



Outside Illinois it occurs in all the Great Lakes, in Lake 

 Champlain, in the St. Lawrence River, and in various smaller 

 streams in Quebec, and thence southward to Virginia and the 

 Ohio basin, westward to Kansas and Missouri, and southwest- 

 ward to Alabama and Trinity River in Texas. 



It is sometimes taken on the hook with a worm bait, and it 

 is probably the only one of our darters definitely known as an 

 angler's fish. 



This species is particularly changeable in color, as observed 

 by us in aquarium specimens, the darker tints sometimes deepen- 

 ing to black, and the gold and emerald complexion of the cheeks 

 and opercles becoming extraordinarily bright. It was noticed 

 that the lower part of the transverse bars would sometimes 

 blacken independently of the upper part, giving an appearance 

 of a row of lateral blotches like those of Hadropterus aspro. 



A third of the food of eleven specimens was found by us to 

 consist of crustaceans (mainly Entomostraca) , and the remainder 

 of insects, the latter chiefly Chironomus larvae, larvae of day- 

 flies, and water-bugs {Corixa). 



Genus HADROPTERUS Agassiz 



BLACK-SIDED DARTERS 



Body rather elongate, compressed or not; mouth rather wide, terminal; 

 premaxillaries not protractile; teeth on vomer and usually on palatines; 

 belly with a median series of enlarged ctenoid plates, which in most species 

 fall off at intervals, but are persistent in some; vertebrae (four species) 39 

 to 42 (18 or 19 + 20 to 23); pyloric caeca 2 to 4. Darters of more or less 

 slender and graceful form, of active habits, and of moderately briUiant color- 

 ation; size various, some species reaching a length of 6 to 8 inches, others 

 much smaller; species 11 or 12. 



