Anculosaic of tur Alabama River Drainage 47 



between the shoals a httle below Greensport, St. Clair County, and Pecker- 

 wood Shoals, near the southern end of Talladega County. Shells from Ten 

 Islands Shoals, Lock 2, Hall's Island and "near the mouth of Upper Clear 

 Creek" are very much alike. The Three Island Shoals material contains 

 shells connecting sulcata with lirata and through that species with shozcal- 

 tcrii. This relationship is made plainer by the specimens from Fort William 

 Shoals. The one shell taken at Peckerwood Shoals, while having folds, 

 resembles the smooth forms of showalterii very much. 



In the typical specimens, the ribs vary in size and distance apart. In- 

 dividuals occur the ribs of which are so flattened that in rubbing the linger 

 over the surface of the shell one scarcely feels the sculpture. A juvenile 

 sulcata taken by Mr. Smith has only eight narrow, thin ribs, widely spaced. 

 Another specimen has three strong folds at the shoulder and no more. 

 However, such variation is rare. Sulcata is characteristically strongly rib- 

 bed. The microscopic sculpture is apparently present upon all shells. In 

 the case of the partly smooth forms, this sculpture has a "cross-hatching" 

 effect beautiful under the glass. 



Ten different banding arrangements were observed, the usual arrange- 

 ment being four continuous equidistant bands. Of 81 shells in one lot from 

 Ten Island Shoals, 16 were without bands, 2 had bands upon the epidermis 

 but not in the aperture, 61 had well-defined bands in the aperture and of 

 these last 45 had the arrangement of four bands. In the transition lot from 

 Three Island Shoals, the bands were broken, irregular, following the sides 

 of the ribs and the channels between, the tops of the ribs having only the 

 usual coloring matter of the epidermis. In the Fort Williams Shoals shells, 

 the thin bands are continuous and appear in pairs. The folds of the dark 

 Peckerwood Shoals shell have small, irregularly shaped deposits of coloring 

 matter which show in the aperture as broken bands. 



The columella of most typical sulcata is white to bluish-white, oc- 

 casionally lead-colored above the center, sometimes purple throughout. 

 In the transition forms the purple columella is common, the white compari- 

 tively rare. It would appear as if the juvenile shells of the typical forms 

 had columellae more or less touched with purple, this being overlaid in the 

 adult shell by deposits of pure white enamel. The color of sulcata ranges 

 from the yellowish-brown of material from the upper river localities, 

 through the mottled shells of Three Island and Fort William shoals to the 

 mahogany-brown shell of Peckerwood Shoals. 



The peristome of all the sulcata is very slightly curved, usually crenu- 

 late and rarely smooth-edged. 



The nuclear whorls of sulcata are small for the genus, rather tightly 

 coiled, smooth, elevated. The ribs begin to develop with the second whorl. 

 In the case of a juvenile shell from Fort William Shoals, a carina appears 

 at the top of the second whorl, this quickly taking on the appearance of a 

 typical fold or rib. So far as can be judged from the greatly eroded 

 specimens, the species does not acquire more than five whorls. 



In only two opercula could the spiral lines be traced. This feature seems 

 to consist of two and a quarter widely coiled whorls within the operculum. 



