20 Calvin Goodrich 



Type in the Museum of Zoology, University of Michigan; paratypes in 

 that museum and the Alabama Museum of Natural History. 



This species has two distinct geographical forms. From the first local- 

 ity at which it has been found — between Riverside and Ogletree Island in 

 St Clair County — to Peckerwood Shoals, Talladega County, the species has 

 some of the general characteristics of the picta group, being bright in color, 

 rounded at the base, rather smooth and usually having fine, interrupted lines 

 in place of bands. At Weduska Shoals a decided change is observed. The 

 shell here is medal bronze to olive green in color. The base is sub-angular. 

 Growth lines are raised, often rough. The arrangement of bands, where 

 bands occur, is four — interrupted or continuous. The shell suggests a snr.'Vi 

 A. tacniata Con. While no specimen of this latter form appears to have 

 been collected above Weduska Shoals, occasional specimens of the middle 

 river form have been found from Weduska Shoals to Rutting Ram Shoals, 

 apparently the southernmost point of distribution. 



The sculpture of clipeata varies slightly, some specimens having the 

 folds which are more or less common in this group and others showing a 

 tendency to develop obscure plicae. In a lot from Fort William Shoals, 29 

 individuals had folds upon the surface, 90 were without any and about 

 one shell in fifteen had indications of plicae. Folds and plicae were both 

 generally absent in collecting from Weduska Shoals downward. Of 117 

 shells of one lot from Fort William Shoals, 100 had the characteristic fine 

 lines; 15 had bands, the arrangement being four or a modification of it; 

 two were without lines or bands. A lot from The Bar, Chilton County, had 

 sixteen shells with the four-band formula, the bands broken or continuous, 

 with three modifications of this arrangement, represented by one specimen 

 each. Three shells lacked any bands, and none had lines. From where 

 clipeata is first found to Peckerwood Shoals, the collumella is white with 

 only occasional shells wherein this character was red or salmon. In the 

 lower river forms, the salmon or salmon-orange columella is common to 

 about as many mollusks as the white columella. 



The embryo shell consists of about one and one-half whorls, smooth, 

 loosely coiled and virtually upon the same plane. The adult clipeata, if un- 

 eroded, would probably be found to have five whorls. 



The outstanding feature of this species is the extraordinarily large oper- 

 culum. In specimens in which the opercula have not been removed they are 

 seen to overlap the columella slightly, touching the edge of the outer lip 

 and occupying practically the whole space of the aperture. Probably in life 

 the operculum is not withdrawn more than one or two millimeters. Some 

 unimportant variations have been observed. At Peckerwood Shoals, the 

 operculum of the adult shell is thin and amber-brown as in the young. The 

 basal margin seldom seems to suffer from abrasion as it does in opercula of 

 many other species. The area of attachment, elliptical in shape, occupies 

 about one-half of the operculum. Frequently the spiral lines seemed to be 

 as strongly developed on the inner side as on the outer. 



