OF CON^CHOLOGY. 125 



2. Geographical Distribution. — We have, in North America, 

 nearl}^ five hundred recognized species, of the shells belonging 

 to the various genera of Strepomatidx. So considerable a 

 moiety of these are found to be inhabitants of the upper 

 Tennessee Kiver and its branches in East Tennessee and North 

 Alabama, and of the Coosa River in the latter State, that we 

 quite agree with Mr. Lea in regarding that region as the great 

 centre of this kind of animal life. We have ascertained that, 

 leaving out the species inhabiting the Pacific States and those 

 which in the descriptions have their habitats designated by 

 States only,* of the remainder, full two-thirds belong to the 

 above two streams ; including three entire genera, nearly all 

 the species in several others, and a majority of the species of 

 every genus except one (Meseschiza,) of a single species. 



The Strepomatidw do not appear to flourish in the neigh- 

 borhood of the sea, and nowhere have the species been found 

 numerous within a hundred miles of our coasts ; nor do they 

 approach the more northern latitudes of tlie Middle and 

 Western States, very few species being found so far north as 

 the Ohio River. 



The Mississippi River also, seems to have formed, from the 

 junction of the Ohio until its mouth, an insurmountable bar- 

 rier to the geographical dispersion of these shells. 



Thus, we find the district of our country, which they inhabit 

 in such profuse numbers of species and individuals, to be 

 really oi somewhat limited extent, and may give its boundaries 

 as follows: — North, the Tennessee River and tributaries. The 

 Cumberland Mountains prevent the dispersion of the species 

 of this river to the northward until its course is directed into 

 Alabama. Here the character of its species (which we shall 

 again allude to further on,) changes, and they become gradu- 

 ally less numerous and of greater geographical dispersion, as 

 the river runs towards the west. J^ast, the mountain range of 

 the Blue Ridge, running southwestwardly into the interior of 

 Northern Georgia. Thence, the Chattahoochee River and tri- 

 butaries, to within about a hundred miles of the Gulf South, 

 the species are restrained from spreading by the influence of the 

 Gulf of Mexico. West, the Alabama, CahaAvba and Black 

 Warrior Rivers and their tributaries, those of the latter reach- 

 ing almost to Florence, on the Tennessee River, which may re- 

 present the northwestern point of our boundary. 



These limits are necessarily imperfect, but nevertheless in- 

 clude at least three-fourths of our species within an area of 

 three hundred miles extent, either north and south, or east and 

 west. 



* As the localities of nearly all of these are " Tennessee" or " Alahama," 

 the most of them also were probably obtained from the Tennessee and 

 Coosa Rivers. 



