32 Calvin Goodrich 



the shell. The growth lines are crossed by very delicate, microscopic revolving striae, 

 waving, broken, absent on some parts of the shell. Suture a little irregular. Aper- 

 ture ovate. Columella moderately stout, rounded except on the outer edge at the 

 center where it is flattened. Peristome sharp-edged, but firm, a little curved close to 

 the suture. 



Operculum: Dark, rather thick, lines of growth very fine, rest scars not heavy. 

 Size 5 mm, by 3^4 mm. Apex rounded. Curves of left and right margins nearly 

 equal. The base of the operculum of the type is lighter colored and thinner than the 

 rest of the operculum, indicating that it has been renewed after injury or wear. 

 The polar point is small, very slightly raised above the plane of the operculum. It 

 is on the left margin hear the base. One and one-half whorls of the closely-coiled 

 spiral development are traceable. The area of attachment is elliptical, the edges 

 thickened with dark callous. 



Measurements: Altitude, 13^ mm.; diameter, 10 mm. Aperture— altitude, 6K 

 mm, ; diameter, 5 mm. 



Type locality: Coosa River, near mouth of Yellowleaf Creek, Chilton County, 

 Alabama. T. H. Aldrich, collector. 



The type is in the Museum of Zoology, University of Michigan; paratypes in 

 that museum and the Alabama Museuin of Natural History. 



This is a localized race, being apparently confined to one shoal of the 

 Coosa River. It has the general appearance of A. facniata Conrad, but it 

 is uniformly smaller, less shouldered, flatter of base. The affinities seem 

 to be closer to A. griff ithiana Lea, which it resembles in form, in both the 

 normal and the produced opercula, and in the tendency to develop the folds 

 characteristic of the griffithiana most common to collections. There are 

 specimens which are hard to distinguish from A. coosaensis Lea and some 

 of the young are very like the juveniles of ,^. ligata Anth. Aldrichi is a good 

 illustration both of the variability of these Coosa race^g and the marked 

 habit of any given form of Pleuroceridae in any one locality to resemble all 

 other forms there. 



The microscopic sculpture varies in strength and it sometimes occurs that 

 the longitudinal lines are less prominent than the revolving lines. Speci- 

 mens with folds are not uncommon, but the variation from flat and scarcely 

 perceptible elevations to rib-like folds, and their irregularity in many in- 

 .stances probably argues that the character is not fixed or directly in- 

 heritable. Material with plicae is comparatively rare, and where it occurs 

 the plications consist merely of low, flattened nodules made a little strik- 

 ing to the eye by spots of dark coloring matter between them. 



The color of aldrichi varies from yellow to dark brown, olive-green 

 specimens being not uncommon. The larger number of individuals is band- 

 ed, and often these bands coalesce so that the epidermis has a "zebra" efifect. 

 The prevailing banding arrangement is four continuous or broken lines of 

 color, variations consisting of modifications of this formula. In one lot, 

 III shells had four bands, mostly discontinuous and frequently with the two' 

 inner bands joined or nearly so; 13 had one or more bands suppressed; 74 

 had bands in the epidermis that did not a])pcar in the aperture; 8 were with- 

 out any bands. 



The embryo shell is very small, smooth, tightly coiled, only slightlv 

 elevated. The unerodcd adult would probably have five whorls. 



The operculum of the type resembles most of the opercula examined. 



