Strophia polita Maynard, 1896

Original Description

"62. STROPHIA MARMORATA POLITA. Novo.

Polished Strophia.

Plate III, Fig. 3, front, fig. 4, side view of type.

DESCRIPTION.

            Size, medium. Shell, rather thick and heavy. Striations, absent. Whirls, 9, the upper, including margin, being about equal in length to all of the others put together. Examined 25 specimens.

            Form of shell, cylindrical, with the first three whirls equal in diameter, and from this the shell slopes to an obtuse point, forming an angle of sixty-five degrees. The shell is quite smooth being marked by some few, fine, but irregular lines of growth, which become rather more prominent on the upper whirl. The whirls are somewhat bulging with the suture rather deep.

            Aperture, rather large and open, scarcely contracted within. The lower tooth is quite prominent, about .05 high nearly twice as long as high, accompanied on the left side by another tooth which is about half its height, yet which is as long as it, but which as it proceeds backward, diverges from it by curving around toward the column, thus the interior termination of the two teeth are nearly .10 apart and considerably widened. Both teeth are set back nearly twice their length, from the frontal bar and taken together are about central in position. The upper tooth is placed well up in the column, quite behind the outer termination of the lower tooth, is about as high as the larger, but rather thinner and extends around the column.

            The margin is not produced forward beyond the diameter of the shell, is very slightly inclined backward and a little to one side, but not much beyond the diameter of the shell; it is thin, measuring about .05, is somewhat reflexed outward, about .04, and rolled over a little, but the edge is smooth. The frontal bar is quite well developed, and although it completely interrupts the striations, they can be seen through the translucent layer within it.

            Color of shell, externally, yellowish white, marked with undulating longitudinal lines of yellowish brown which are more abundant on the spiral whirls, where many are as wide as the white interspaces between them. These lines are seldom broken by horizontal encroachments of white. Within, pale yellowish brown, becoming white on the teeth and margin.

DIMENSIONS.

            Size of type 1.05 by .45. Largest specimen 1.25 by .50; smallest 1.00 by .40. Longest specimen, 1.25; shortest, 1.00. Greatest diameter, .50; smallest .40.

OBSERVATIONS.

            Variation consists in specimens being either lighter or darker than the type, in other words, the markings are more or less abundant, thus covering more or less of the surface of the shell. There is one distinct form as given below.

            Form No. 1. Larger than the type, 1.25 by .50, otherwise similar.

            This well marked sub-species differs from typical S. marmorata in the absence of striations, in the more cylindrical form of the shell, in the singularly diverging double teeth, and less converging margin. It is with considerable hesitation that I do not admit this form to full specific rank, but as I find some individuals which show evidence of intergradation, and as I found them in the same tray with the specimens of S. marmorata, described above, and consequently labeled as coming from the same locality (Carbo Cruz, Cuba.) I have thought it best for the present to consider them as sub-species only.

            The difference in the teeth given above, in two such closely allies forms as S. marmorata and S. m. polita is worthy of note, as it exactly coincides with the theory, which I have had occasion to mention that the teeth of the members of this genus are vital characters, for as the animals have no muscles which grow to the shell anywhere, they depend largely upon the teeth as a means for holding themselves on the shell, therefore, with any change of environment, which would tend to alter the weight of the shell would also tend to change the form of teeth. In the accompanying cut fig. 2 A. I give a figure of the teeth of S. marmorata and at ib. B, the same of S. polita.

            There is a group of land shells which occur in the island of Mauritius, now included in the family Pupidae, which are closely allied to Strophia, and which possess similar teeth. In these shells the evolution of the teeth, both upper and lower, is clearly indicated. At first it is evident that the margin about the aperture was projected forward all around, when the animal for some reason lost its attachment for the shell, and required a tooth, then a portion of the margin, below the mouth, was bent inward, afterwards becoming detached to form a tooth; afterwards a second was formed in a similar way." (Maynard, 1896:14-15)

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