the late Professor E. Forbes in the Quarterly Journal of the Geological
Society of London, for August, 1852. In the opinion of the last-
named author ‘ a closer geographical relationship between the African
and American continents than now maintains is dimly indicated’ by
the marine mollusks of St. Helena; and ‘the information we have
obtained respecting the extinct and existing terrestrial mollusks of
this isolated fragment of land would seem to point in the same direction,
and assuredly to indicate a closer geographical alliance between
St. Helena and the west [? east] coasts of South America than now
holds.1 And in the*Report of the British Association for 1851 will
he found an abstract of a paper by the same distinguished naturalist,
entitled, ‘ On some Indications of the Molluscous Fauna of the Azores
and St. Helena.1 I t is here stated that ‘ the marine mollusks [of
St. Helena] would seem to point to the submergence of a tract of land
probably linking Africa and South America before the elevation of
St. Helena. Along the sea-coast of such a tract of land the creatures
common to the West Indies and Senegal might have been diffused.1
I am not quite satisfied with this hypothesis, and I believe that more
information is needed to support it. Some of the land-shells of St.
Helena are European, and may have been introduced by the agency
of man; others are peculiar to the Island. A few of the marine
shells are Mediterranean, while the greater number are well-known
inhabitants of the Indian Ocean and the West Indies; all these
may have originated anywhere. But it must be borne in mind that
St. Helena is separated from Africa and South America in every
direction by very deep water, which is nowhere less than 2000
fathoms or 12,000 feet. I t therefore seems scarcely probable that
such an abyssal and extensive tract of the sea-bed could have been
dry land or ‘sea-coast,1 in a geologically recent period, so as thus to
account for the diffusion of littoral species such as Mytilus edulis, M.
crenatus, and Littorina striata. I should be rather inclined to
attribute the present distribution of the marine fauna of St. Helena
(not to a supposed continuity of land between Africa and South
America in that or any other direction, hut) to the action and
influence of the great Agulhas Current, which issues from the Indian
Ocean and flows round the Cape of Good Hope northwards towards
St. Helena, and thence past Ascension to the West Indies. The
partial correspondence between the Mollusca of the Indian Ocean
and of the Mediterranean may have been owing to the Guinea
V U l lU U U j CIO VV V jll coo
in the line of the Sahara—a very wide tract, which certainly was
submerged during the quaternary period. I.must admit, however,
that our information as to the marine Mollusca of the South-
Atlantic region, including St. Helena, is very scanty and unsatisfactory.
The only dredging that has ever, to my knowledge, been attempted
off St. Helena was made by Dr. Wallich in 1857, on his return home
from In d ia ; and this was at a depth of from twenty to thirty fathoms.
I t produced a few small shells, which Dr. Wallich kindly gave me.
Many of these appear to be undescribed species. The promised
circumnavigation expedition, under the auspices of the Royal
Society, will doubtless enable us to learn something of the South-
Atlantic fauna.
‘Mr. Edgar Smith will describe such of the speoies, and those
dredged by Dr. Wallich, as are new to science.”
Of the land-shells eleven species are now found in a living state, the
rest are all in a more or less subfossil condition, embedded in the superficial
soils of the upper parts of the Island, varying at heights of 1200
to 1700 feet above the. sea, and entirely confined to the north-eastern
quarter of the Island. Mr. Darwin, who visited the Island thirty-eight
years ago, attributes their extinction possibly to the loss of food
and shelter they experienced by the destruction of the native woods
which occurred during the early part of last century, when the old
trees died and were not replaced by young ones, these being destroyed
B H H IM I and h°gs’ which had run wild in numbers from the year
¡1502. The state of the shells and the positions in which they
are now found on the barren parts of the Island seem to indicate
that such was the case with the last surviving members of the
family, but I am inclined to date the commencement of their decline
to a more ancient penod-viz., that time when those parts where the
W M H P y were swamPS clothed with vegetation and such
elements as were essential to the existence of BuMmi, but which, as the
Island became smaller through the encroachments of the sea lost
' f e h/ dramage and consequently with it their vegetation
and suitability to sustain snail life. vegetation
These beds of extinct land-shells, which occur chiefly on Flagstaff
Journal of Besearches, By Charles Darwin, M.A., F.B.S., p. 582.
I 2