1 78 Branley A. Branson 



Etheostoma camurum (Cope), E. variatum Kirtland, E. spectabile 

 (Agassiz), Ammocrypta pellucida (Putnam), and Percina copelandi 

 (Jordan) from the White River in Indiana, as well as the minnows 

 Hybopsis dissimilis (Kirtland) and Notropis ariommus (Cope), and the 

 sucker Erimyzon oblongus (Mitchill), most of these doubtless re-invading 

 during post-glacial times via the Ohio River. The Wabash River, how- 

 ever, has been the principal Low Plateau pathway of piscine re-invasion 

 into Indiana and Illinois (Table 4). 



At least one species in this area, Clinostomus funduloides Girard, 

 reported from the Lower Tennessee (Miller 1978), Cumberland (Burr 

 1980), and Little Sandy rivers and several other streams in northeast 

 Kentucky (Bauer and Branson 1979), the Wabash drainage in Indiana 

 (Lee et al. 1980; Gerking 1945; Blatchley 1938), and the Barren and 

 Green rivers (Retzer et al. 1983), has a strongly pre-glacial relict distri- 

 bution. This may be true also of Rhinichthys atratulus. 



Fishes considered by Etnier (unpublished) to have strong lowland 

 and Lower Mississippi affinities are presented in Table 5. In addition, 

 he believes that several species of Low Plateau fishes are derivable from 

 areas west of the Mississippi, from the Ozarkian and Great Plains fau- 

 nal regions: Hybopsis gracilis (Richardson), H. storeriana (Kirtland), 

 Hybognathus hayi Jordan, H. nuchalis Agassiz, H. placitus Girard, 

 Notropis lutrensis (Baird and Girard), N. camurus (Jordan and Meek), 

 N umbratilis (Girard), N. fumeus Evermann, and N. stramineus (Cope). 

 Such faunal exchanges could have occurred either via the aforemen- 

 tioned isthmus across southern Illinois and Indiana, or via the 

 Mississippi-Ohio system. To this list should be added the percid subge- 

 nus Nothonotus (Zorach 1972; Harker et al. 1980) (see discussion 

 below). 



Although many fish species enjoy wide distribution throughout the 

 Low Plateau, many others are restricted to certain portions of the area. 

 One of the most interesting of such patterned distributions is endemic- 

 ity, important in biogeographic studies and presenting several implica- 

 tions. Applied specifically to the Interior Low Plateau aquatic problem, 

 endemicity may reflect interrupted gene flow imposed by isolation 

 resulting from drainage modification and control (cut off from sur- 

 rounding drainages) by master rivers like the Green (Kuehne 1966) and 

 extralimital origins, dispersal into other drainages and modification and 

 divergence in the new system. For example, Zorach (1972) proposed 

 that the ancestral stock of Nothonotus arose west of the Mississippi in 

 the Arkansas or Red River systems and dispersed from there into the 

 Ohio and Tennessee systems, where evolutionary divergence occurred. 

 The Tennessee and Middle Cumberland, and the Green-Barren rivers, 

 seem to have been of great importance as speciation centers. Three dif- 



