MONOGRAPH OF THE GENUS STROPHIA, 
3 
Genus STROPHIA Albers. 
Gen. Ch. Shell, varying in form from oblong-oval to cylindrical, 
but the width is never more than half the length and usually less, some- 
times being only one third. The apex is pointed, occasionally obtusely, 
but the angle never measures more than 90 degrees, and when acute, it 
is never less than 50 degrees. The whirls vary from nine to twelve, the 
lower are very narrow but they rapidly become wider as they ascend, 
the last, with the margin of the aperture, occupying about one-half of 
the length of the shell. The whirls are usually furnished with promi- 
nent perpendicular striations, but are occasionally smooth. The mar- 
gin of the aperture is quite prominent, produced forward so that the face is 
parallel with the sides of the shell, with the edges rolled backward and 
often thickened. Crossing the lower portion of the aperture, inclined 
downward to the right, is a more or less prominent frontal bar that con- 
nects the lower parts of the margin. The aperture narrows quite rap- 
idly within, and there is a prominent tooth near the center of the lower 
wall and usually a second one on the column; this latter named is not 
always present. Young shells which are incomplete, inasmuch as the 
aperture is not surrounded with a margin that is produced forward, as 
in the adult, and which consist of fewer whirls, more or less, accord- 
ing to age, have as a rule, five teeth, of which two are on the upper 
wall, two on the lower wall, and one on the column. These teeth become 
absorbed as the shell grows and others take their place further in advance, 
hence, if they be well within the aperture, they are often less than 
the normal number. The spirally ascending, parietal walls are very 
thin, Plate II, lc, while the wall of the hollow column, Plate II, lo, 
which opens outwardly, back of the left of the aperture, is also thin. 
On the other hand, the outer walls which are made up of at least two 
layers, the outer calcareous and the inner more horny, are thick and often 
quite massive. In size the shells vary from .60 in length by. 25 in diam- 
eter, to 2.60 by .60, with all gradations between. 
In color, outwardly the shells are usually white, often flecked or 
striped with purple, reddish purple, or rosy; inwardly they are either 
roseate or purplish of varying shades. 
The animal is not large for the size of the shell, the foot, with head 
and eye peduncles, being about as long as the shell. The foot is slender, 
narrower than the aperture, about two thirds as long as the shell; beneath, 
it is smooth and provided with numerous pores that exude a mucous 
with which the animal lubricates the surface over which it glides. The 
