Madeiran Helmet Snail (Leiostyla cassida)
The Madeiran Helmet Snail was described in 1852 on the basis a single specimen, that had been collected in 1830, the species was later found again in quite large numbers in several areas on the northeast and the southeast part of Madeira.
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See Thomas Vernon Wollaston in the year 1878 (Testacea Atlantica).:
“Until within a comparatively recent period the P. cassida, although abounding in the subfossiliferous beds at Caniçal, was considered of the utmost rarity as a member of the present fauna; but it was nevertheless met with in tolerable profusion by myself and the late Rev. W. J. Armitage, during March 1849, at the extreme head of the Ribeira de Sta. Luzia, in the south of Madeira proper (in the exact spot where the original and then unique example was taken by Mr. Lowe, on April 13th, 1830), – namely, amongst vegetable detritus, on the steep buttress, or bank, immediately to the right of the waterfall, and which constitutes the base of the lofty perpendicular rocks; and it has subsequently been obtained by Mr. Leacock, the Rev. R. B. Watson, and others, in the same locality. It occurs however likewise in the north of the island, having been taken by the late Mr. Bewicke in the Ribeira de São Jorge; so that in all probability it will be found to be pretty generally distributed in the damp sylvan ravines of intermediate altitudes.”
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The shell reached a height of about 0,46 cm.
The last live individuals had obviously been found in the year 1870.
All of the known former localities are more or less urbanized today and recent searches (last in 2008) failed to find even a single living individual.
The Madeiran Helmet Snail therefore is now regarded most probably extinct.
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References:
[1] T. Vernon Wollaston: Testacea Atlantica: or the Land and Freshwater Shells of the Azores, Madeiras, Salvages, Canaries, Cape Verdes, and Saint Helena. London: L. Reeve & Co. 1878
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(public domain)
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edited: 29.01.2011