Pupa incana Binney, 1851

Original Description


Gray Strophia.

Plate VII, 20 & 20A, shell: Fig. 13, A, front, B, right side;

PUPA INCANA Binney, Terr. Moll. N. A., I p. 109; III, 1851.


            SP. CH. Size, small. Shell, thin. Striations, absent. Teeth, two, both short and not prominent. Whirls, 11. Examined 1,000 spec­imens.

            Form of shell, cylindrical, with the first two whirls equal in diameter and the third is slightly smaller and the fourth is a little less in size, from this, the shell tapers to a blunt point, forming an angle of 65 degrees. The lines of growth are only faintly defined, but as­sume more prominence on the back of the upper whirl. Sutures, not deep.

            Aperture, large, open, measuring a little more just within than at the entrance. The lower tooth is not prominent, .02 high by.08 long, and its position is just a little to the right of the center; the upper is a mere protuberance, yet makes a complete turn around the column.

            Margin, not produced forward beyond the diameter of the shell, nor is inclined to either side, is very thin, measuring only. 02, and the edges are slightly rolled backward. Frontal bar, not well developed.

            Color of shell, externally, grayish white throughout; internally, yellowish white.


            Size of type; 1.05by.40. Largest specimen, 1.07 by .67; smallest, .67 by .35. Greatest diameter, .41; smallest, .30. Longest specimen, 1.05; shortest, .67.


            As shown under Dimensions, there is great variation in size, in this species. This extreme difference has caused me considerable perplexity, for this seems to indicate much more than individual variation, and, in fact, rather more than varietal difference. These extremes represent two forms which show in the hundreds of specimens examined, but a small percentage of gradation. Then the smaller form is smoother and whiter, with the first three whirls nearly, equal in diameter; all are more bulging, and only 10 in number. These characters certainly show

a strong tendency toward assuming specific rank, and with complete isolation from the larger form, would soon become fixed enough to war­rant a name, but as the shells inhabit a very limited area, I leave them as they are for the present, under the name of S. incana.

            Mr. W. C. Binney in "Land and Fresh Water Shells of N. A.," page 247, says that he has seen a variety of S. incana with longitudinal markings; in this, however, I cannot well avoid thinking him mistaken, some other species evidently being indicated. In his quotation of local­ity of specimens, he gives Key Biscayne, Fla., and from this island he may have got his colored specimens. As this latter named place is over 100 miles, in a; direct line, from Key West, with numerous water ways through which the tides sweep with great force, between, this dis­tance would afford more than sufficient isolation for the evolution of a

distinct species, even if the original stock were S. incana. This seems to be a matter that requires special investigation, and for further re­marks upon this subject see under head of Observations in forthcoming species.

            Known from all other species, by the absence of striations, white color, with the very pale interior, small size, thin shell, and short teeth,


            The Gray Strophias occur in a limited area, on the island of Key West, Florida. According to my experience they are restricted to that portion of the northern side of the key that lies between the salt ponds and the Gulf of Mexico. In habit they are somewhat peculiar, as many hybernate beneath stones, and as spring advances, emerge to feed upon the short herbage that grows rather scatteringly in the section in which they live.

            This species is said to occur in Cuba also, but I have never seen a specimen from that island, nor have I ever met with it on other of the Florida Keys."

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