38 CAI.VIX Goodrich 



seems most reasonable at this time is that the species is a rehc of a race 

 dating far back in geological time and in the comparatively recent and quite 

 noticable evolutionary alteration of the Coosa mollusca it has disappeared 

 from that stream except at Wetumpka, holding its own only in the tribu- 

 taries. The ancient lineage of ampla is possibly indicated in the shell itself, 

 some juvenile forms of it having characteristics strikingly resembling A. 

 praerosa Say of the Tennessee system. 



The usual form of ampla is subglobose. the aperture ovately rounded, the 

 body whorl shouldered at the suture and there often bearing folds and plicae. 

 Yet in nearly all lots of INIr. Smith's collection many specimens appear which 

 are conic, the aperture narrowly ovate or even elliptical, the surface wholly 

 free of folds and plicae. The pronounced sculpture is more common to the 

 shells of the Cahaba than to the material from the Coosa creeks. Where 

 folds and plicae both occur the region near the suture is usually broken by 

 nodules or tubercles, resembling in this regard A. plicata Conrad of the 

 Black Warrior. In the creek forms these characters vary with localities — 

 being a marked feature, for instance, of the Canoe Creek specimens and 

 entirely absent from the Waxahatchee, Buxahatchee and Warson collections. 

 The growth lines of ampla are rather strong, the revolving lines usually 

 obscure or often absent. 



The species is yellow, dark brown or olive green. The creek forms are 

 easily distinguished from those of the rivers by being brighter, the epidermis 

 having escaped the erosion from sand and the common accidents of heavy 

 currents. About fifteen different arrangements of bands were observed in 

 this study, but most of them were merely modifications of the prevailing 

 formula of four equidistant, interrupted or continuous bands. The creek 

 forms show no marked difference in this character from those of the rivers, 

 though unhanded specimens appear to be rarer in the creeks than in the 

 other localities. In one lot of 224 specimens from Lily Shoals of the 

 Cahaba, 33 were without bands. 



The inner edge of the columella of ampla is ridged rather than rounded 

 as in other groups of Anculosae. This is plainer in young and half-grown 

 specimens than in the adult. It is not usually flattened on the outer edge, 

 though one lot of creek shells shows this characteristic in virtually all the 

 specimens. The lower third of the columella is produced or flattened as if 

 smoothed with a palate knife. In color the columella is white, red or purple, 

 this last color being the most common. Occasional lots, as those from the 

 Coosa at Wetumpka, have the columella white. The peristome is sharp- 

 edged, firm, usually straight as if the animal held itself tightly to flat stones. 

 The embryo shell is small, smooth, elevated, rounded and apparently 

 consists of two whorls. I\Iost of the juveniles collected by Mr. Smith 

 have the usual Anculosa form, but specimens from Wetumpka are very much 

 flattened of apex and have the aperture flaring like Neritina. Juveniles 

 taken in Waxahatchee Creek and in the Cahaba River at Ccnterville bear two 

 carinae at the periphery as in the young of A. praerosa Say. 



The operculum of ampla is dark red to brown, somewhat broader in 

 proportion to length than in the case of A. taeniata Conrad. The apex is 



