2 U.S. NATIONAL MUSEUM BULLETIN 282 



distributed and are thus infrequently obtained except in intensive 

 survey work. One, Noturus flavipinnis has not been collected since 

 1893. The known localities from which it was obtained are now 

 ecologically unsuitable for its existence and it may be extinct. Although 

 not often encountered, the members of the genus become rather widely 

 known because of the painful "sting" produced by their pectoral spines. 



The study of the variation and distribution of populations in Noturus 

 has revealed several interesting patterns and presented problems of 

 interpretation. Some wide ranging species, particularly miurus and 

 insignis, show relatively little structural change geographically, but 

 several structures in Noturus gyrinus gradually increase in length and 

 number from north to south. Similarly a west to east increase is ap- 

 parent in pectoral rays of Noturus leptacanthus and in anal rays of 

 Noturus funebris. The presence of highly variant populations of 

 Noturus nocturnus in the Red River system, which is in the middle 

 of its range, is puzzling. In a number of species, localized and relatively 

 minor variation is noted. 



Three clusters of species, each with closely related allopatric repre- 

 sentatives, are recognized as species groups; other species groups are 

 suggested but the relationship of the species is not as clear. These 

 allopatric populations are recognized as species because they show a 

 relative morphological uniformity, with consistent divergence from 

 related populations; trends or gradation of characters from one popula- 

 tion toward the other do not exist and intermediates or intergrades 

 are lacking. 



Natural hybrids between species of Noturus are described but hy- 

 bridization is rare. Sexual dimorphism in the family, once thought to 

 be important in the interpretation of species of Noturus, has been 

 exaggerated ; instead differential morphological change, accompanying 

 growth and sexual maturity, has resulted in several unnecessary names 

 in Ictalurus, complicating its nomenclature. 



Acknowledgments 



A great many individuals have contributed importantly to this 

 study in many ways, especially by the loan of specimens or making 

 them available for study, provision of laboratory space, aid in col- 

 lecting specimens, or have given freely information about specimens, 

 notes on specimens in their care, or data from writings unavailable 

 to me. To each I am greatly indebted and I sincerely trust that no 

 one has been overlooked: Reeve M. Bailey, Marie-Louise Bauchot, 

 Norman Benson, the late Leon Bertin, Albert P. Blair, James E. 

 Bohlke, E. Milby Burton, Robert S. Campbell, Jorge Carranza, 

 William M. Clay, Robert E. Cleary, Bruce B. Collette, the late 



