172 Branley A. Branson 



Goniobasis laqueata (Say), common in the Tennessee River basin 

 (TV A 1975) and Cumberland River (Branson and Batch 1982), is 

 another species that has spread into various segments of the Interior 

 Low Plateau drainages from the Tennessee basin. Goniobasis semicarin- 

 ata has its center of distribution in the Kentucky River drainage (Bran- 

 son and Batch 1981). It entered the Cumberland River (Branson and 

 Batch 1982), possibly by stream capture such as that documented by 

 Kuehne and Bailey (1961), and the Salt River of Kentucky and the 

 Wabash of Indiana (Goodrich 1935), perhaps by tributary hopping and 

 reinvasion. 



Many additional examples in the Pleuroceridae and Unionidae 

 illustrate the principles involved, but the ones presented here shall suf- 

 fice. From the very rich centers of endemicity in the Alabama-Coosa 

 system and secondary speciation centers in the Tennessee and Middle 

 Cumberland systems, the Pleuroceridae and Viviparidae (Somatogyrus, 

 Viviparus, Campeloma) expanded northward and westward into the 

 Cumberland, Green and Lower Tennessee rivers, and via them into the 

 Ohio River basin. Depauperacy is one of the main features in the north- 

 ern part of the area. The Tennessee and Cumberland rivers served as 

 major refugia for unionid species that later reinvaded upstream Ohioan 

 streams, and the Green River may have served as a refugium as well. All 

 three rivers were sources for repopulation of the Wabash and Maumee 

 rivers in postglacial times (Johnson 1980). Pleurocerids were able to 

 reinvade Ohio and Indiana from similar sources via the Ohio River, 

 penetrating into the Wabash River and its tributaries. Or perhaps, as 

 discussed below, they came from some of the other old tributaries of the 

 Teays system. 



FISHES 



Fish and mollusk distributional patterns in the Interior Low Pla- 

 teau must be correlated with various physical and hydrologic phenom- 

 ena in order to account for observed faunal relationships between 

 drainage basins. According to Lachner and Jenkins (1971), there are 

 four principal ways that aquatic organisms have achieved or may 

 achieve new dispersal distributions: (a) stream capture, (b) eustatic 

 changes in coastal plains, (c) Pleistocene modifications of drainages, 

 and (d) movements from one drainage to another via past and existing 

 interconnecting main streams. These mechanisms were perhaps involved 

 in structuring the fauna of the Interior Low Plateau. Pleistocene glacia- 

 tion certainly affected the region, very obviously so in the Shawnee 

 Hills, the northern boundary of which (38th parallel) is demarked by 

 glacial till (Harker et al. 1980, and literature cited therein). In this same 

 general area, numerous karsts and faults crisscross the Green, Pond, 

 Tradewater, Rough, Barren, and Ohio rivers. 



