26 U.S. NATIONAL MUSEUM BULLETIN 2 82 



of points and is the only Noturus that has gotten into the Hudson 

 Bay drainage. 



An indication of a similar, but more southern, distribution is shown 

 by the ranges of the four species of the juriosus species group in the 

 subgenus Rabida. In this group Noturus Juriosus is the sole species 

 of the subgenus that is found in Atlantic coast streams; Noturus 

 munitus ranges farther east along the Gulf coast than do others; 

 these combined with the species in the Ohio and Arkansas drainages 

 point to an ancestor that was widely distributed around, but that did 

 not extensively enter, the eastern upland region. Noturus gilberti 

 in Virginia, and Noturus albater in the Ozarks are relicts without 

 apparent close relatives elsewhere. 



Sexual Dimorphism 



Breeding ictalurid catfishes may temporarily show marked sexual 

 differences, but young and immature individuals of both sexes are 

 essentially alike in color and gross morphology. Ripe females are 

 heavy with eggs and, if young adults, may lack the excessive devel- 

 opment of head musculature and dark color displayed by nest-guard- 

 ing males. With age, the female's musculatiu"e and color progressively 

 resemble those of the mature male. Spawning males thus are commonly 

 darker or more drab than spawning females. In some forms the external 

 genitalia are useful in distinguishing the sexes, at least at the time 

 of maximum gonad development. Some of these evidences of sexual 

 dimorphism have played an important part in the interpretation of 

 species of catfishes, especially in Ictalurus, and led to identification 

 of two species of Noturus as one. Prominent, permanent, external, 

 sexual differences have not been found in Noturus, and aside from the 

 genitalia, may not exist in the other genera. There is some evidence 

 suggesting slight external sexual differences in all groups. The only 

 reliable way that was found to determine sex in Noturus was by 

 examination of the gonads, as attempts to sort various species by 

 sex on the basis of external morphology and genitalia met with 

 failure. 



A few years ago several workers accepted the suggestion that gross 

 sexual dimorphism is a common permanent phenomemon in catfishes 

 and is involved in the proper delineation of species. This belief was 

 largely based on statements by Hvibbs (1940, pp. 209-211) and Hubbs 

 and Allen (1944, p. 118) and complicated by the frequent observation 

 of a young appearing female, which often more or less resembles the 

 immature young male, spawning with a more fully developed, dark, 

 puffy cheeked male. These developmental changes have confused the 

 nomenclature of several of the species of Ictalurus with excess names 



