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U.S. NATIONAL MUSEUM BULLETIN 282. 



Map 4. — Distribution of Noturus nodurnus Jordan and Gilbert. The circles represent 

 localities from which I have examined specimens. All unverified literature records are 

 from well within the area of the figures shown. 



Relationships. — Noturus nocturnus appears to be most closely- 

 related to Noturus insignis, from which it differs in the fewer hypurals, 

 the shorter anal fin, the poorly serrated pectoral spine, the poor 

 development of black margins on the vertical fins, the relatively short 

 chunky body, and the rounded head. These characters, however, are 

 subject to considerable variation from population to population in 

 both species. The two species are strikingly similar in structure of the 

 pectoral spine, the number of fin rays, the tendency to have dark 

 marginal or submarginal bands on the vertical fins, the sensory canal 

 system, and show resemblances in ecology. They seem to form a 

 compact and closely related group allied to Noturus funebris and 

 Noturus phaeus. 



Ecology. — This species lives in moderate size to large streams in 

 riffles or in areas of moderate to fast current over a gravel and boulder 

 bottom. It is seldom found in streams with shifting sand bottoms. The 



