Strophia carlotta Maynard, 1894

Original Description

"44 STROPHIA CARLOTTA Novo.

Ft. Charlotte Strophia.

Fig. 49, A, front, B, side view, of type.

DESCRIPTION.

SP. CH. Size, small. Shell, rather thin. Striations, present. Whirls, nine. Examined 1,000 specimens.

 

            Form of shell, oval, with the first whirl the largest, the second is but little smaller, then the shell slopes gradually to a rather blunt point, forming an angle of seventy degrees.  The striations are quite numerous, twenty-four on the first whirl, they are a little narrower than the interspaces between them, are beautifully rounded being about one half as high as wide and, considerably polished. They are straight and slightly inclined from right to left.

            Aperture, placed near the center of the shell, is not large, arched, short, about as high as wide and not much contracted at the entrance. Lower tooth, not prominent, .03 high, narrow, not as wide at high and about twice as long as high, is set back about once its length from the frontal bar, and is not elevated. The upper is about one half as large, is placed low, not once its width from the floor of the cavity.

            Margin, not produced forward quite as far as the diameter of the shell, is a little thicker than the shell behind it, is slightly beveled into a blunt edge, but this is not produced backward.  The frontal bar is not very well developed, although it completely crosses the aperture, yet the striations are indicated within it.

            Color of shell, reddish brown, externally, with the striations paler. Pale brown internally, becoming paler on the teeth and magrin [sic].

 

DIMENSIONS.

Size of type, .85 by .40. Largest specimen, 1.00 by .43; smallest, .72 by .35. Longest specimen, 1.00; shortest, .72. Greatest diameter, .43 ; smallest, .35.

 

OBSERVATIONS.

Individual variation is toward a form with a thickened margin, that is beveled and grooved, in this respect resembling the margin of a fossil form (S. agassizi) recently described by Dall (Bulletin Mus. Comp. Zool. Vol. XXV, 1894, p. 122) as coming from the aeolian limestone, of the top of the quarry, about a mile east of Ft. Charlotte, While S. agassizi may be the remote ancestor of this species, it is probable that it has passed through several species since then. S.  agassizi has no striations, but I have found a large fossil Strophia. scattered through the aeolian limestone of the surface of New Provi­dence, in the neighborhood of Nassau, which is more probably the immediate ancestor of S. carlotta. Individual variation is also toward producing a form with coarser, more widely-apart, striations. Indivi­duals of this kind were doubtless the origin of  S. neglecta, for S. neglecta, although such a strongly marked species, has some characters in common with S. carlotta, such as general form, wide, low aperture, nine whirls, and the peculiar form of the striations, which in S. carlotta are, as nearly as possible, half pillars, recalling at once the beautifully-polished striations of S. albea from Spruce Key.  Those striations appear of the same general form in neglecta and through it in S. n. agava, but they are broken and somewhat roughened in S. neglecta, They have, however, in a measure, regained their original form in S. n. agava. Besides these individual variations, we find two well-marked forms.

No. 1. A dwarf form, the smallest given in Dimensions. Whirls, eight, and striations, eighteen to the first whirl, otherwise the same as in the type.

No.2 is larger, with nine whirls, thicker margin, and with a heavier shell. This form in some respects resembles S. n. agava and was it not for the fact that it differs in color, and has a lower, wider aperture, resembling the type S. carlotta, and that S. n. agava inter­grades directly with S. neglecta, it might be supposed to be the direct origin of the Agava Strophia.

            The Fort Charlotte Strophia may be known by the peculiar oval form, less wide aperture, and reddish color. This species resembles S. glans more than it does any other shell in form, but in S. glans the shell is white, and the aperture rather higher than wide and the margin thicker.

HABITS AND DISTRIBUTION.

Strophia carlotta occurs in the immediate vicinity of Fort Charlotte, New Providence. The type locality is at the foot of the hill, on which the fort stands, on the north side. Here they were found on low bushes and herbage. Further up the hill toward the fort, almost under the shadow of the walls of the small old Spanish fort, which stands a little to the eastward of the large structure, occurred the small form No. 1.

To the westward of the type locality, nearer the bushes and among them we collected the larger form No.2.

I think the origin of the dwarf form can be traced directly to the dryness of the soil on the hill top. At the time of my visit in March, 1893, the foliage of the shrubbery was so parched with heat and lack of moisture that it crumbled in the hand. We have seen another instance where a dwarf form has been produced by a dry environment in Strophia nana, on Little Cayman, but the extreme pigmy size of this species was also probably due, partly, to feeding upon a peculiar plant. See VoL 1 of these contributions, page 27." Maynard, 19894:154-156)

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