Tennessee River and Crawfish Distribution 



141 



M ' s so Ur , 



/ 



Gulf of Mexico 



Fig. 10. Distribution of Hobbseus. Arrow as in Figure 1. Stippling = H. 

 orconectoides. 



pleopod; the appendage in each has an attenuated tip; and both have a 

 carinate rostrum. Several western species have caudal projections of the 

 sternite just anterior to the annulus, which partially obscure the recepta- 

 cle, but none is developed in the same way or to the degree as is the case 

 in P. (Pe.) versutus. It is unique in the subgenus in retaining a strong 

 spine on the basis of the cheliped. Despite considerable geographic vari- 

 ation, the species stands alone. It is confined to areas younger than 

 Grim's (1936) "Eocene." Does it represent a third line of proto-Pennides 

 descendants, is it a Miocene phenomenon, or is it both of the preceding? 

 Moving to a second subgenus of Procambarus, Scapulicambarus, 

 another pattern related to post-Miocene development can be seen. Only 

 P. (S.) clarkii (and one other, below) is found significantly outside the 

 southern Atlantic Coastal Plain or the Flint-Chattahoochie basin (Fig. 

 11). The easternmost limit of this species is in Escambia County, 

 Florida, and where it traverses the coast it is in post-Miocene areas. 

 Again, its dispersal seems to be a post-Miocene event. As its relatives 

 are all in the extreme southeastern United States, an origin in that area 

 is not unreasonable. Equally, a post-Miocene origin is feasible. But 

 since the species has spread as far as Mexico (Hobbs 1962b) in such a 



