Anculosae of the Alabama River Drainage 



37 



mens, rather rare, vary somewhat from typical forms, but are quite recogniz- 

 able. 



The operculum of hrevispira is very small in proportion to the aperture. 

 As seen in the shell it lies close to the columella, the apex fitting into the 

 corner between the columella and peristome with a little room to spare. 

 At the base, however, is a wide gap and nearly one-third of the aperture 

 betw^een the right margin of the operculum and the peristome is left unpro- 

 tected. 



Fort William Shoals 



Anculosa ampla Anthony 



Fig. 23 



Anculosa ampla Anth., Annals N. Y. Lye Nat. Hist., VI, p. 158, pi. v, fig. 22, 23, 

 Oct. 1855. 



Anculosa clegans Anth., Proc. Acad. Nat. Sci., Phila., Feb. i860, p. 69. 



In point of distribution this species is one of the most interesting and 

 certainly the most puzzling of the Anculosae of the Alabama drainage. It 

 is the characteristic member of the genus in the Cahaba River. In the Coosa 

 it has been found sparingly at Wetumpka, close to the mouth of that river, 

 and there only. But north of Wetumpka the species has been collected in 

 five western and three eastern tributaries of the Coosa. 



Not another Anculosa of the drainage has so strange a distribution. If 

 this were due to environmental requirements on the part of the species, one 

 might expect to find a similarity in the habitats of ampla. There is anything 

 except similarity. In the Cahaba drainage the species occupies not merely 

 the parts which are river-like in character, but also the upper reaches where 

 the conditions are those of a creek, the Little Cahaba River which is more 

 creek than river, and a mineral spring five miles from Centerville which is 

 on the Cahaba. The difference between the Coosa tributaries and the Coosa 

 proper at Wetumpka is that between small streams with lively but not very 

 heavy current and a large river with a strong and, for many months in the 

 year, a deep current. Other Anculosae of the Alabama system are distribut- 

 ed with known or apparent continuity. For example, A. downiei Lea lives 

 in the Coosa drainage from the Conasauga to just beyond the middle Coosa 

 Shoals, A taeniata Conrad from the middle Coosa to Clairborne on the 

 Alabama. 



The explanation for the unusual distributional record of ampla which 



