Tennessee River and Crawfish Distribution 



Ss o Ur , 



139 



Fig. 9. Distribution of Faxonella. Arrow as in Figure 1. Horizontal rulings = 

 Fx. clypeata. 



that part of its range (Fig. 9). Other, apparently later-differentiating 

 species of other taxa, which have similar environmental habits and 

 cohabit successfully with Faxonella elsewhere, are not so widely distrib- 

 uted. Thus, such a distribution as exhibited by Fx. clypeata, a relatively 

 advanced member of the genus, argues for an Eocene origin for the 

 genus. 



Hobbseus orconectoides Fitzpatrick and Payne, the most primitive 

 member of that genus, occurs in streams associated with Midway 

 (Paleocene) deposits (Fig. 10). The other species occur up and down the 

 Tombigbee drainage, except for one just across the divide in the head- 

 waters of the Pearl drainage. As May (1981) and Murphey and Grissin- 

 ger (1981) suggested that surface materials analyzed by Grim (1936) 

 represent post-Eocene alluvium rather than primary deposits, the above 

 areas could easily be considerably younger than proposed. One cannot 

 escape the close relationship between H. orconectoides habitat and the 

 delta of Grim's (1936) "river of considerable size" or "late Eocene" 

 (probably Miocene). The intimate association of the genus with the 

 Tombigbee drainage makes one suspect that some members of the 

 archiorconectoid stock became isolated in the lower reaches of the river 



