168 U.S. NATIONAL MUSEUM BULLETIN 2 82 



may raise questions as to the proper systematic level (species or 

 subspecies?). No intergradation or significant geographic gradients 

 are known and the hiatus in ranges is probably real. The criterion of 

 interbreeding cannot be applied because the forms are found in three 

 completely isolated watersheds. The two forms (N. placidus and 

 N. stigmosus) that occur in the Mississippi drainage are apparently 

 not only segregated geographically, but separated ecologically by a 

 barrier (the lower Arkansas and Mississippi Rivers) of highly turbid 

 waters and shifting sand; morphologically they are quite dissimilar. 

 Noturus stigmosus appears to be more closely related to A^. munitus 

 than to the other species, suggesting relatively recent isolation of the 

 two forms. 



In comparison with other Noturus, only N. gyrinus occupies as 

 extensive a range as does the furiosus group. The species of the group 

 are all characteristic of lowland streams, chiefly large streams and 

 rivers; thus simple headwater crossovers between streams probably 

 did not take place. Instead, relict populations of a more widely 

 distributed ancestor remain today, or the forms attained their present 

 distribution through changed drainage of major streams. No direct 

 method of getting into the eastern Carolina streams from the Ohio 

 Valley or Gulf coastal region is evident, thus the geographic pattern 

 suggests a more widespread previous distribution. Noturus munitus, 

 however, due to closer similarity to N. stigmosus than to the other 

 forms, may have become established relatively recently, perhaps 

 during some excessive overflow of glacial meltwaters from an over- 

 burdened Mississippi River, or during a concentration of these fresh 

 waters in the Gulf of Mexico between the mouths of the Mississippi 

 and Alabama Rivers. Because other large-river fishes are known to 

 range eastward from the Mississippi River into other Gulf coastal 

 streams, a major change in the course of a stream may be indicated. 

 Invasion of the Lake Erie drainage by N. stigmosus has been recent as 

 indicated by the similarity of the Huron River and Ohio Valley 

 populations, and by their distribution. It undoubtedly took place in 

 post-Wisconsin time through the Maumee glacial outlet. 



Noturus placidus, new species 



NEOSHO MADTOM 



Plates 4 (fig. 9), 15 (fig. 2), 17 (fig. 2); Map 13 



Noturus miurus Jordan [misidentification]. — ? Gilbert, 1886, p. 207 (Neosho R., 



Emporia, Kans.). 

 Schilbeodes miurus (Jordan) [misidentifications]. — Breukelman, 1940b, p. 381 



(Neosho R. system,* Kans.). — Moore and Paden, 1950, p. 87 (lUinois R., 



about 5 mi. NE. of Gore,* Okla.). 



♦Material indicated by an asterisk has been re-examined. 



