"STROPHIA PILSBRYI Novo.
Pilsbry's Strophia,
Fig. 55. A, front, B, side view of type.
DESCRIPTION.
SP. CH. Size, medium. Shell, rather thin and light. Striations,
present. Whirls, ten. Examined 125.
Form of shell, an elongated pointed oval, the first whirl being the largest, the second, third and fourth being successively a little smaller, then the shell slopes a little more rapidly to an acute point, forming an angle of sixty-three degrees, The first whirl is short, equalling in width the next four. The striations are not numerous, twenty-two to the first whirl, are a little narrower than the interspaces between them, inclined to be angular, slightly ridged, with ridges of growth between them are not very regular, not at all arranged in lines and not in the least inclined, being straight from the upper whirl to the apex.
Aperture, quite small, open, not at all inclined to the right. Lower tooth, not prominent, triangular, being as wide as high, and a little longer than wide. It is very slightly elevated, and set back from the frontal bar not quite its length.
Margin, single, not produced forward quite as far as the diameter
of the shell, it is thin, a little thicker than the shell behind it, is smoothly rounded, and produced backward into a blunt edge, While the frontal bar is quite well developed, it does not project much beyond the striations.
Color of shell, externally, pale ashy blue, becoming horn color on
the apex, and waxy white on the margin, which extends backward
past the teeth when the shell becomes quite abruptly brown, with
almost a sharp line of demarkation.
DIMENSIONS.
Size of type, 1.07 by .45. Largest specimen, 1.09 by .45; smallest, .87 by .37. Longest specimen, 1.09; shortest, .87. Greatest diameter, .45 ; smallest, .37.
OBSERVATIONS.
Individual variation is not great. As might be expected, there is some marks of reversion toward the type form, which, as I shall clearly show, must have been S. bimarginata, and this reversion takes the form which we should most expect, that of the double tooth, but this is never as marked as in typical S. bimarginata, and out of the one hundred and twenty-five examined I have found twenty only, and in more than one half of these the central tooth had the slightest indication only of the doubling.
This double tooth is never accompanied by the double margin, and the only indication of the feature so prominent in S. bimarginata is a slight furrowing of a thickened and beveled margin in some specimens.
There is a decided inclination to produce a form with fewer striations, some, in fact, being nearly smooth on the upper whirl.
There is one decided form, and that is one in which although the form has not changed, the color has become reddish ash throughout, striations and all. This color appears in intermediate specimens on the apex, thence gradually spreads, through other specimens, over the entire shell. Some adults are slightly flecked. This is the form through which the sub-species next described, S, p. evolva, was derived.
I have named this interesting species of Strophia for Mr. A. H. Pilsbry, the accomplished curator of conchology at the Academy of Natural Sciences, Philadelphia.
HABITS AND DISTRIBU1'ION.
I have said that Little Galden Key lies at the entrance of Middle Bight, and about a half mile directly west of it is a long, narrow islet, called Goat Key, thus it is situated well within the Bight; but owing to the trend of the southern shore of the Bight it is quite near this portion of the main island. The key is only about one eighth of a mile long, and nowhere over fifty yards wide. This little spot of land, however, is of great interest from a conchological point of view, for it not only contains two distinct species of Strophia and one sub-species, but these forms are in themselves remarkably interesting, as will be seen.
So important is this Key, and the Strophias which live upon it, that I have given a little chart of it (See Fig. 56) which, although accurate enough, perhaps, for the purpose for which it is intended, must be regarded simply as a diagram.
As will be seen by consulting the figure, also, the key is nearly divided into two parts, these two parts being connected, in fact, by a narrow sand bar over which the water flows during very high tides. The easternmost portion is surrounded by a sand beach, but the central portion is higher and is covered by a spare growth of bushes. This portion of the key is the home of Pilsbry's Strophia, but it was not common there at the time of our visit in April, 1893. The form No, 1, which I have indicated, occurred toward the western end of this portion. I have noted the range of the Strophias by a number of Us."
