50 Calvin Gcxjdkich 



Though idea's niiclca is credited to the Coosa River there is good reason 

 for beHeving that the species is confined to the Cahaba River and its tribu- 

 taries. Lea received his material from Dr. Schowalter, and all the compacta 

 which have been found in the Schowalter collection are assigned to the 

 Cahaba. 



The sculpture of compacta consists simply of fine growth lines, often 

 worn nearly smooth. No revolving lines can be made out with a glass of 

 ordinary power. Color varies from yellow to dark brown. Green shells, es- 

 pecially among the juveniles are fairly common. Bands, where they appear, 

 are three in number, equidistant, varying slightly in width and depth of 

 coloration. Only one banded specimen was found which difl^ered from this 

 formula, the variation consisting merely of the absence of the basal band. 

 The two shells collected by Mr. Smith in the Cahaba at Henry Ellen were 

 without bands. Of one lot of four specimens from Lily Shoals, one only was 

 .without bands. In the second lot from this locality, 85 had bands, 26 were 

 without them. 



The columella of compacta is small, smooth, rounded, angulated at the 

 center rather than rounded. A callous just below the turn is sometimes 

 sufficiently heavy so as to suggest a "tooth"'. In color the columella is us- 

 ually white, often marked with purple or red. The Calkins lot has 4 

 specimens with white columellae ; 3 the columellae of which are entirely 

 purple; 5 with the columella part white, part a faded purple. In the larger 

 Lily Shoals lot, white is the predominant color 



The form of the species varies slightly. The periphery is frequently 

 subangulated, far more often rounded. A few have the constriction of the 

 body whorl so characteristic of A. ligata. In one lot, several specimens 

 have the narrowed aperture and produced peristome of the species known 

 as Goniobasis loiiist'illensis Lea, which is probably a Lithasia. Shells with 

 the apex entire are wholly absent from this collection, but from specimens 

 only partly eroded six whorls for a fully grown compacta are indicated. 



A form of the species from Buck Creek, a tributary of the Cahaba in 

 Shelby County, is light yellow, flat of whorls, almost pyramidial and 

 without bands. This creek form is exceedingly puzzling because of its 

 resemblance to Goniobasis germana Anth. and close study is required to 

 separate the two. This is another illustration of the meager barrier which 

 separates some of the genera of the Pleuroceridae. 



The operculum is small, thin, ovate, red. Growth lines and rest scars 

 are rather heavy. Apex rounded, the right and left margins about equally 

 curved. The right margin is thin, the left margin firm. The polar point is 

 very small and near the base of the left margin. The whorls within the 

 body of the operculum are closely coiled., and in the specimen illustrated 

 the total number of whorls is four — an irregularity comparable with an 

 instance occuring in picta. Compared with the operculum of melanoides, 

 that of this species is darker, heavier, more ovate, the growth lines heavier, 

 the polar point more distinct. Judged by the opercula, the relationship be- 

 tween mttata and melanoides is closer than the connection between either 

 of these species and compacta. 



