44 Calvin Goodrich 



The size of the ribs of any individual sulcate shell may differ, and in one lot 

 the number of ribs per individual varied from six to fifteen ; in the same 

 lot three juvenile shells had each six ribs. In partly grown specimens the 

 ribs are undercut, i. e., the base of the rib is smaller than the outer surface. 

 As the animal matures base and edge of the rib are on the same plane. 

 A\'here the ribs fall below six in number there is usually a decrease in their 

 size or strength, and in such instances the sculpture is best described as 

 folds. In material from Fort William Shoals were mollusks with folds 

 at the top of the whorl, becoming obsolete before the periphery is reached; 

 specimens with folds at the suture and upon the base, the space between 

 being smooth; shells with just the suggestion of folds which were confined 

 to the top of the whorl. Fine growth lines crossed by straight or waving 

 revolving lines appear on virtually all the specimens. They are shown most 

 strikingly on the smooth forms, giving the epidermis the silky appearance 

 characteristic of A. ligata Anth. 



Ordinarily the body color of shozvalterii is very dark brown, but shells 

 occur which are straw color, some somewhat mottled and a few in which the 

 ribs have a lighter color than the interspaces. The bands tend to follow the 

 ribs, but the coloring matter is sometimes absent and in other instances 

 it is spread through the shell material irregularly. In one lot from the 

 Schowalter collection, there are seven specimens without bands to eight 

 having bands. The usual arrangement is four, rather heavy, equidistant 

 bands. 



The columella of old shells is heavy, rounded. Shells with a white colu- 

 mella occur, but in most shells it is stained with brown or purple. The 

 crenulate outer lip of which Lea speaks is found ordinarily only in the 

 younger shells, the furrows within the aperture seldom exceeding three mm. 

 in length. As the animal grows older it fills these channels. The peristome 

 has a slight curve at the suture in numbers of the specimens, but usually 

 it is straight and in certain examples almost appressed, as if the habitat 

 were very swift water and the animal clung tightly to the face of the rocks. 

 The color of the aperture is white, reddish, dark red and sometimes almost 

 black. 



The embryo consists of about one and one-quarter whorls, quite loosely 

 coiled, in the same plane and widening suddenly at the aperture. As near as 

 can be made out from this material, a perfect, uneroded, adult would not 

 exceed four whorls. 



The operculum is of moderate thickness, dark brown or red, nearly twice 

 as long as it is wide. Lines of growth are strong, but not coarse. The left 

 margin is thickened, as is also the right margin in the opercula of old shells; 

 in the young it is thin and usually torn. The left margin is nearly straight, 

 the right curved, the apex not very pointed, the basal margin broadly round- 

 ed. Normally the polar point is close to the base of the left margin, but 

 in old and worn specimens this position has shifted toward the center of 

 the basal margin. On none of the material examined could the spiral lines 

 be traced. 



