Cerion restricta Maynard, 1894

Original Description

"STROPHIA RESTRICTA Novo.

Restricted Strophia.

Fig. 58. A, front view, B. side view, of type.

DESCRIPTION.

            SP. CH. Size, very small. Shell, rather heavy and thick.

Striations,present. Whirls, nine. Examined seventy-five specimens.

            Form of shell, an elongated oval, the first and second whirls being about equal in diameter, the third is a little smaller, then the shell slopes to a rather acute point, forming an angle of fifty-eight degrees. The striations are quite numerous, nineteen to the first whirl, are about as wide as the interspaces between them, are beautifully rounded and polished, very regular and arranged in lines.

            Aperture, very small, not quite as wide as one half of the shell, arched, and about as high as wide. Lower tooth, not prominent, about .03 high, as wide as high, and about twice

as long as high. It is not elevated, and is set back nearly once its length from the frontal bar. Upper tooth, absent.

            Margin produced forward about as far as the diameter of the shell, it is nearly straight and not inclined to the right. It is about as thick as the shell behind it, beveled below on either side, marked with fine lines of growth, but doubled above with

lines of growth between the two divisions. The frontal bar is well developed, and protrudes beyond the striations, and is but little inclined.

            Color of shell, externally, ashy white, mottled, but not trans­versely, with reddish brown. Internally, brown, rather dark in shade, extending quite to the margin, but this and the tooth are paler.

DIMENSIONS.

            Size of type, .75 by .32. Largest specimen, .92 by .37; smallest, .62. by .32. Greatest diameter, .37; smallest, .32. Longest specimen, .92; shortest, .62.

OBSERVATIONS.

            Variation is toward a slightly larger form, but with about the same proportion, but with a leveled margin with lines of growth only, also toward a more pointed form with the first whirl the largest. There is also the following distinct form:

            No.1. White in color, and with a tendency to assume a less number of striations. The margin is beveled and grooved, but in some individuals is doubled.

            This singular little Strophia may be distinguished from S. thorndikei, which it resembles somewhat, by the heavier shell, thicker margin, smaller aperture and different color. I know of no other Strophia which it resembles.

HABITS AND DISTRIBUTIUN.

            About midway on the southern side of the western portion of Goat Key is a little bay, and on the western border of it is a small mangrove swamp. A sand beach entirely surrounds this portion of the key, hut along the little bay, especially to the eastward of the mangrove swamp, the land being low (for the mangrove swamp evidently repre­sents an old lagoon) the sand has encroacher} upon the land considerably. This sandy tract, however, in the immediate neighbor­hood, is covered with bushes, or small trees. It was on one of these little trees and on a few shrubs very near it that I found the colony of the singular little Strophia restricta.

            On Goat Key one can learn a lesson in the evolution of species of Strophia which will prove of great value to him. Here on this little spot of land, at most not over three acres, we find three distinct forms of this genus of shells; and be it remembered that this island is distant from Little Galden Key only about a half mile, yet, as seen, it is impossible to assign even characters which will define a form to the Strophias which live on Green and Little Galden Keys, and these islands are about fifteen miles apart! Facts like these have already caused me to remark that I feel that it is far too early in my studies of this genus to even speculate on the origin of many of the species, and more especially on the origin of all the groups, and their connection with one another.

            One thing is clear, however, that the Strophias inhabiting Goat Key were derived directly from the S. bimarginata of Little Galden Key. First, S. pilsbryi, through this the dark, flecked S. p. evolva, and this sub-species gave rise, most strangely, to the little dwarf, S. restricta. The most sceptical regarding the value of color as a specific character has only to visit this key and note the transition of S. pilsbryi into its sub-specific form, with its accompanying correlative

characters, while the little S. restricta exhibits clearly how closely one species may live to another and yet be distinct. The sand from which grew the tree and bushes on which I found S. restricta isolated this form as completely, if not more so, than if miles of ocean rolled between them.

            I have said under the Habits of Strophia nana (Vol. I Contribu­tions, page 28) that this Strophia had the most limited distribution of any animal with which I was acquainted, but in this respect it must yield the palm to S. restricta, for this species was confined to a single tree and the bushes that came in direct contact with it, in fact, all of the specimens which I collected I gathered without moving a single step."

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