182 Branley A. Branson 



Alabama, and Western Kentucky, from whence it has been able to 

 extend its range up the Ohio into the Wabash River drainage of Illinois 

 and Indiana, the Green River of Kentucky, and old Teays tributaries 

 (Kentucky and Big Sandy rivers) in eastern Kentucky. Noturus phaeus 

 Taylor and N. hildebrandi (Bailey and Taylor) have ranges that only 

 impinge upon the Low Plateau in Mississippi River drainages of north- 

 ern Alabama and western Tennessee, N. phaeus barely getting into 

 southwestern Kentucky (Terrapin Creek) (Taylor 1979). Noturus flavus, 

 being more tolerant of cold water, is distributed throughout much of the 

 upper two-thirds of the Mississippi drainage, including most of the Low 

 Plateau. Noturus elegans Taylor, autochthonous to the Barren-Green 

 system of Kentucky and adjacent Tennessee, has an apparently disjunct 

 population in the Tennessee River basin (Duck River). In the Low Pla- 

 teau, N. eleutherus occurs in the Tennessee (no published records from 

 Kentucky stretches of that stream), the Green River, and the Wabash 

 system of Illinois and Indiana. Noturus stigmosus, a member of the 

 furiosus species complex, avoids most of the Low Plateau but has pene- 

 trated into the Green and Salt river drainages of Kentucky and into the 

 Wabash River of Illinois-Indiana. Noturus miurus has the widest distri- 

 bution of all Low Plateau madtoms, having been reported from all 

 drainages. 



It seems likely that the ancestral stock of Noturus arose somewhere 

 in the lowlands of the Mississippi River basin from a bullhead-like 

 ancestor (Taylor 1969), and spread from there into other parts of Amer- 

 ica. Using the Tennessee River basin as a speciation center, additional 

 species diverged and spread widely throughout the system in pre- and 

 postglacial times, particularly after development of the Upper Ohio sys- 

 tem. Such conclusions are supported by the paucity of Noturus species 

 in the Eastern Seaboard drainages. 



The occurrence of Moxostoma {Thoburnia) atrippine Bailey — a 

 close relative of the torrent suckers of Virginia — in the Barren River 

 system of the Low Plateau either represents a relict or a case of immi- 

 gration, extinction in intervening areas, and survival and divergence. 

 The wide hiatus in ranges between population centers in the subgenus 

 Thoburnia suggest the latter. 



CONCLUSIONS 



The examples of Interior Low Plateau aquatic biota discussed here 

 merely represent the complexity of the mechanics and biologistics of 

 understanding such a fauna and flora. I have not discussed other taxa, 

 such as the swarms of unionid pelecypods and decapod crustaceans, 

 because that would have lengthened the paper considerably. However, 

 the distributional patterns of these interesting organisms also very 

 graphically reflect similar conclusions. 



