Anculosae of the; Alabama River Drainage 21 



Measurements of shells: 



Altitude Diameter 



A mm. Three Island Shoals, Talladega County 



Fort William Shoals, 



Peckerwood Shoals, 



Weduska Shoals, Shelby County. 



Near mouth Waxahatchee Creek, Shelby County 



The Bar, Chilton County 

 15 1014 



14 10 Butting Ram Shoals, Coosa County 



This species, so far as tlie records show, is confined to the Coosa River, 

 reaches its maximum development at Fort WilHam Shoals — judging by 

 size and the quantity of material collected — and disappears with the end of 

 Butting Ram Shoals. 



Anculosa dozvniei Lea 

 Figs. I, 2 



Anculosa doumiei Lea, Proc. Acad. Nat. Sci., Phila., 1868, p. 153. 



The highest place in the Coosa drainage at which Mr. Smith collected 

 this species was in the Conasauga River, east of Dalton where the stream 

 forms the border between the two Georgia counties of Whitfield and Mur- 

 ray. The one shell collected there, though apparently adult, was only 11 1-2 

 mm. in height by 8 mm. in diameter. Near Tilton, in the same river and 

 about fifteen miles farther down, the largest shell was 10 1-2 by 7 1-2 mm. 

 At his next station, Resaca, Gordon County, Ga., ]\Ir. Smith's largest 

 downiei measured 12x91-2 mm. 



In the Oostanaula River, the continuation of the Conasauga, the shells 

 have reached an extreme of 14 1-2 x 10 mm. At Rome, Ga., where the 

 Oostanaula and the Etowah rivers join to form the Coosa, the largest shell 

 has the measurements 15 x 10 mm. But up the Etowah at Kingston, about 

 thirty miles above Rome, the size has a^ain dwindled, the largest downiei 

 collected being 12 x 5 1-2 mm. 



This is an excellent illustration of a rule often recited that the size of 

 fresh water mollusks frequently bears a ratio to the size of the body of 

 water inhabited. The reasons seem clear. The upper reaches of a river 

 are in the stage of a creek, being subjected to greater relative variations 

 than the stream farther down. The waters become low in the dry seasons, 

 warm, often stagnant, charged with the gases of vegetable decay. 

 The soluble foreign material brought into the creek by brooks becomes more 

 highly concentrated than in the true river. The Anculosae, which ordinarily 

 move about very little, are forced into an unnatural energy as a measure 

 of self-preservation. There are alterations in the quantity of food supplies, 

 probably alterations in the quaHty of this food, certainly decided changes 

 in the chemical constituents of the water. Circumstances dictate a smaller 

 animal and therefore a smaller protective shell. 



