Strophia agrestina Maynard, 1894

Original Description

"STROPHIA AGRESTINA Novo.

Grass Strophia.

Fig. 60. A, front view, B. side view, of type. C, margin, Form No.3.

DESCRIPTION.

            SP. CH. Size, small. Shell, very thin and fragile. Striations

numerous and small, but perfect. Whirls, nine. Examined 1,000 specimens.

            Form of shell, quite cylindrical, but with the first whirl a little

smaller than the second and third, which are equal in diameter, then the

shell slopes to a blunt point, forming an angle of sixty-five degrees. Sec­tions between the whirls very shallow. Whirls not bulging. The striations are numerous, thirty-seven to the first whirl, they are small, less than half

cylinders, but rounded and perfect for their entire length, and slightly in­clined from right to left, and are a little wider than the interspaces between them, while the entire shell is polished.

            Aperture, very small and open, elongated and arched, but scarcely higher than wide. Lower tooth, about .02 high, about as narrow as high and three times as long as high and is set back a little more than its length from the frontal bar. Upper tooth absent.

            Margin not produced forward quite as far as the diameter of the shell, it is thin, not as thick as the shell behind it, is smoothly rounded in front, and rolled backward into a blunt, but well-developed, edge. The frontal bar is only slightly indicated, but completely inter­rupts the striations.

            Color of shell, creamy white, externally, marked with wide, rather

continuous lines of reddish brown. Pale brown, within, fading into creamy white on the margin, leaving the tooth white, in contrast with the dark surrounding.

DIMENSIONS

Size of type, .87 by .35. Largest specimen, 1.10 by .40; smallest, .55 by .32. Greatest diameter, .42; smallest, .32. Longest specimen, 1.10; shortest, .55.

OBSERVATIONS.

            The young of this species have, as a single tooth, the upper; this is singular, as mature shells, with rare exceptions, have no trace of this tooth.

            Individual variation is considerable; in one direction it is toward a form, with a larger, more rounded orifice; shells like this are inclined to have the upper whirl larger than the others, also all the whirls bulge slightly. On the other hand there is a shorter form, with straight whirls. A color variation is towards a paler form with the white predominating. As the reverse of this, I have a single specimen of a beautiful chestnut brown throughout, slightly streaked with creamy.

This specimen has assumed correlative characters and is thicker with a more contracted orifice, and it is cylindrical in form, the first four whirls being equal in character. Besides these variations, which may be considered as purely individual, we find the following three well­ defined forms:

            No.1. A dwarf form with eight whirls, size. .55 by .30, other­ wise as in the type. This form is largely represented, at least twenty per cent. of the whole number, and I have reasons for believing that the tendency of the entire species is in this direction.

            No.2, a large form, 1.10 by .32, rather cylindrical with the first four whirls equal in diameter, with the shell thicker, and the orifice large. This form is quite largely represented, but as most of the specimens are dead shells, many of which I did not collect, I cannot give the exact percentages. The tendency is for this form to pass out of existence, or in other words, the species has passed through this form and is becoming smaller.

            No.3 is a singular form, with the first whirl decidedly smaller, and the aperture nearly central, disproportionately elongated, consider­ably higher than wide and with the first whirl quite small (See fig. 60, c). This form is so pronounced that it is quite likely to become specific in time.

            This is not the Pupa martensiana of Wienland (See remarks on this head under Observations in S. eximea) yet it is so labelled in many collections which I have examined. This shell is very thin and fragile, so thin, in fact, that the striations can be plainly seen through it, when looking in at the aperture. I have never seen any other shell which resembles the Strophia agrestina, even belonging to this sub-genus, in this respect. The large form of S. agrestina and small specimens of S. eximea are alike in size, but differ so utterly, as described, as to be at once distinguishable, but the best character,aside from the thinness of the shell, in the Grass Strophia, is the absence of the frontal bar, this being quite well developed on either side in S. eximea.

            Before closing this article I want to add a few words in regard to the shell named Pupa martensi Weind, inasmuch as this name and that of P. martensiana are often confused, and I have even seen speci­mens of Strophia agrestina labelled as S. martensi.

            S. martensi is a very peculiar shell, differing from most species of the striated Strophias in having a regular constriction to the striations, near the sutures, thus somewhat isolating a series of rounded knobs above each suture (there may, however, be more than one species so characterized), resembling, somewhat, a form of the little S. nana, figured on Plate II, fig. 11, n. Vol. 1, of these Contributions (See also description, page 28).

HABITS AND DISTRIBUTIUN.

            The Grass Strophia occurs on the south side of New Providence, about opposite of the city of Nassau but distant from it some six miles. They live in pine woods, among which grow scattering palms, about a half mile from the shore, and occur under stones, fallen palm leaves, shrubs, etc., or are found clinging in clusters among the tufts of grass of which there is a scanty growth in this locality. I cannot give the exact range of this species, but I have traced it for several hundred yards along the two roads which go to the south side beach. I have found them on two occasions, one in February, 1884, and then in March, 1893. On both occasions they were quite abundant."

 

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