Strophia tracta Maynard, 1894

Original Description


Mottled Strophia.

Fig. 37, A, front view of type.


            SP. CH. Size, about medium. Shell, rather thin. Striations present. Whirls, ten. Examined, 300.

            Form of shell, a pointed cylinder, the first whirl being the largest, then each successive whirl is a little smaller than that above it, to the fifth whirl, when the shell slopes to a rather acute point, forming an angle of fifty-eight degrees. The striations are rather numerous, twenty-six on the first whirl, are not prominent, are quite regular, but not arranged in lines. They are very smooth, not furrowed, and just about as wide as the interspaces between them.

            Aperture, rather small, a little contracted at the entrance. Lower tooth small, about .03 high, not as long as high, and but slightly elevated, and is about central in position. The upper tooth is represented by a slight protuberance.

            Margin, produced forward about as far as the diameter of the shell, is very slightly inclined to the right, a trifle beyond the diameter of the shell, is slightly thickened, measuring about .04, and while the posterior portion is

produced backward into a blunt edge, it is not rolled over. The

frontal bar is narrow, yet interrupts the striations, which are, however, slightly indicated within.

            Color of shell, creamy white, beautifully mottled and flecked with yellowish brown and umber, the markings often crossing the striations. Within, deep umber brown, paler on the central tooth and fading rather abruptly into creamy white on the edge of the margin.


            Size of type, 1.05 by .45. Largest specimen, 1.02 by .47; smallest, .75 by .37. Longest specimen, 1.25; shortest, .75. Greatest diameter, .47; smallest, .37.


            While the type form preserves its identity, and prevails in numbers, this is one of the most unsettled forms of Strophia that I have seen, as it has developed no less than five distinct forms, besides a small percentage of specimens showing complete gradations with typical S. cinerea. The forms are as follows:

            No. 1. A long cylindrical form, with the first three whirls equal in diameter. Otherwise as in the type. Size 1,25 by .42.

            No.2. A color form nearly white, or with a few pale mottlings, otherwise as in the type.

            No.3. Form and size about as in the type, but very dark brown throughout, with white striations, which are more numerous, being twenty-five or more.

            No.4 is a small form, .75 by .37, with nine whirls only, but the margin is considerably thickened, and the color pale, with few or no fleckings. Nos. 1, 2, and 3 are not very common, constituting about three per cent. of the whole; of No.4 there are about six per cent.

            No.5 is the. most remarkable of all, being pure ivory white in color, externally and internally, with a thickened margin (about .07), and open aperture. Striations coarse and flattened, twenty to the first whirl. Both teeth are very prominent. Size, 1.00 by .37. This form recalls No.3 of S. cinerea, but is smaller, heavier, and whiter. I have four shells only, and did not three of them show some gradations toward form No.4, I should not hesitate to pronounce it a distinct species, as it is very far removed from the type. Further investiga­tions in the neighborhood of the type location of S c. tracta may reveal a fixed locality for this shell.


            I found the Mottled Strophia quite common in a very restricted location on the borders of a field, that is situated nearly on the extreme eastern point of Hog Island. Here they were clinging to the grass and herbage, but I did not then observe any fixed location for the various forms. I should judge that the form was of quite recent origin, and has not yet become settled."

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