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Cymba melo, Pecten polymorphus, and Panopœa Aldebrandi, are met with as far as the neighbourhood of Lisbon. The fine Chiton rufus, the largest European representative of the genus, I have only obtained in Lisbon and Vigo, and am not aware of its being recorded from any other locality.

The following species range from the southward to the coasts of Gallicia and Asturias :

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Diplodonta rotundata
Galcomma Turtoni
Modiola barbata

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Crenella costulata
rhombea
Avicula Tarentina
Calyptroa Sinensis

(Milford) Emarginula rosea

Turritella tricostalis
Fusus contrarius

Murex Edwardsii
Purpura hæmastoma
Nassa trifasciata

Cassis saburon ?
Triton nodiferum

corrugatum

Of the following species, the most northern known habitat is the south of Great Britain and the coasts of Ireland :

Pholas parva

Cytheria chione, (Car-
narvonshire)

Gastrochna modiolina
Petricola lithophaga
Venerupis irus

Venus verrucosa
Cardium aculeatum
rusticum

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Pandora rostrata (Channel Islands

Lucina divaricata

Diodonta fragilis (Car-
narvonshire)
Syndosmya tenuis
Donax politus

Ervilia castanea

Mactra helvacea

Lutraria oblonga

Tapes decussata (Car

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Pleurotoma elegans
Ringuicula auriculata
Aplysia Patersoni

Haliotis tuberculata

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Trochus exiguus striatus Adeorbis subcarinatus Rissoa lactea striatula Scalaria clathratula

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Chemnitzia scalaris

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fenestrata
Truncatella Montagui
Murex corallinus
Lachesis minima

Nassa pygma
Mangelia gracilis (Clyde )
Ovula patula

narvonshire)

It is a fact to be noted, as probably bearing some relation to an ancient distribution of land, that the range of many species of mollusca, in proceeding northward, takes a curve to the west. Several inhabitants of the Mediterranean, such as Tellina balaustina, Circe minima, Psammobia costulata, Neæra all the species, Mangelia Lefroyii, Marginella læris, &c., touching upon the extremity of Cornwall, and extending round the west of Ireland to the Hebrides, although absent from the Channels and the north sea; also a few species being found common to

the coast of West Africa, the Canary, Madeira, and Azore Islands, which are not to be obtained in Morocco or the south of the European continent.

In treating of the distribution of mollusca, some notice should be taken of species which are considered to be local, that is, limited to a particular locality or a small area, though the number of these is constantly diminishing as we extend our knowledge.

A newly-discovered species is supposed to be confined to the spot where it was first obtained, until it re-appears in a locality where it was perhaps least expected to be met with; this more particularly happens with some of the deep water species. Many marine shells supposed to be peculiar to the Canary Islands are probably common to a large unexplored tract of the African coast-several of them I have found in Madeira.

The interesting shell Pleurotoma, or Mangelia teres, was first discovered by Professor E. Forbes on the coast of Lycia; it was next met with, a few years afterwards, in the Channel of the Minch, between the Isle of Skye and the outer Hebrides, and has since been procured pretty generally throughout the British seas. I have obtained it in various parts of the Mediterranean, in the Canary and Madeira Islands, and it is in Loven's enumeration of the shells of Scandinavia. Crenella rhombea, one of the rarest species of our seas, having been only found in three or four instances and one locality (off Weymouth), I have met with in the Bay of Gibraltar, Gulf of Tunis, and abundantly off Lancerote, one of the Canary Islands. Chemnitzia fenestrata, discovered only six years ago in Dartmouth harbour, has since been obtained from at least two other localities in the South of England; I have procured it in Vigo bay, and it has been found in the result of dredgings from Alexandria in Egypt. It would be easy to cite many similar instances, but what I have mentioned may suffice to prove how unsafe it is to conclude that a species is restricted to a peculiar locality, from the negative fact of its not having been found elsewhere.

For my part, I believe that very few, if any, marine species are confined to very small areas. With reference to the curious mollusk Bifrontia zanclaa, which was only known as a very rare fossil obtained at Messina, and no recent example even of the genus recorded to have been seen, but which I found living in considerable abundance at Madeira, it is probable that further researches will discover its existence in other parts of the Atlantic; if not, it will appear to be an exception, and that its present habitat is its last refuge and stronghold, after becoming elsewhere extinct.

As has been already shown, the Islands of the Canaries, Madeiras, and the Azores possess a marine fauna closely allied to that of the old continent, notwithstanding that the prevailing set of the currents is from America. Very few mollusca are common to both sides of the Atlantic, except such as are inhabitants of the Arctic Seas, and extend along the coasts radiating from that centre. Out of about 160 species of shells of the Canary Islands and Mediterranean, of which I sent specimens to the late Professor C. B. Adams, he informed me that he could only identify one (Columbella cribraria) with a West Indian species-he had probably overlooked Neritina viridis, and perhaps one or two others.

Saxicava arctica appears to be the most cosmopolitan of mollusks; belonging, as its specific name imports, to the Arctic Seas, but able to accommodate itself to a variety of climate, and to all zones of depth, as far as about a hundred fathoms; it has been brought from Spitzbergen, China, Behrings Straits, California, and Australia. This, with perhaps a few others, forms an exception to a general law which appears to limit the range of species in animals of this class.

The distribution of mollusca depending partly on the nature of the sea bottom, and on other conditions difficult of appreciation, is liable to great intervals of space. Neara costellata, inhabiting the Mediterranean, Canaries, Madeira, and Norway, has only been met with at one point (Loch Fyne) between the first and last-mentioned localities, or in about 20 degrees of latitude, and there are other species which present parallel circumstances.

Before concluding, I may be allowed to make a few remarks on the distribution of Land Mollusca, which must, it is evident, be affected by many conditions, different from those which influence the spreading of their marine relatives.

We find among snails and allied genera an astonishing variety of habit. Some affect moist situations and dense forests never penetrated by the rays of the sun, feeding voraciously upon a rank vegetation; while others prefer the most arid tracts, where their food must be scanty and deficient in succulence; some, like Bulimus decollatus, pass most of their time buried in the earth; while others, through winter's cold and summer's parching heat," select exposed situations, and are enabled to retain their vital powers through extreme changes of temperature. Of these our little Helix umbilicata and Helix pisana may be quoted as examples. Most species seek shelter in the crevices of rocks, and under stones.

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Although many terrestrial mollusca are capable of enduring not only extremes of heat and cold, but of existing for an astonishing long period

without food, (properties which, as admirably adapting them for a sea stock upon long voyages, are extensively taken advantage of for that purpose by sailors of the south of Europe; and I may here remark, that as an article of food, the mollusca, with very few exceptions, have been too much neglected by ourselves, and that snails are not only wholesome and nutritious, but even, where prejudices do not interfere, esteemed a delicacy, not to mention that their being in request for culinary purposes would be the means of relieving our gardens from their inroads); notwithstanding, I say, their powers of endurance, they appear to be particular in the selection of locality. The arctic climate and productions are evidently not suited to snailish and sluggish habits and tastes. Even in the colder temperate regions species are few, but increase in numbers as we proceed southward, and they are found particularly to abound in limestone formations.

It is a most remarkable fact connected with the distribution of land shells, that some species are extended over very wide districts, while others are restricted to an area of a few square miles, or even less. Great Britain does not offer for observation a single species which is not likewise an inhabitant of France or Germany, though the neighbouring countries of the continent possess some which are not to be met with in this kingdom; and while thus among the hundreds of islands of Great Britain not one produces a species peculiar to itself, in the groups of the Canaries, Madeiras, and Azores, each island presents some species supposed to be strictly local.

This fact is particularly striking in the Madeiras-where Madeira proper contains but few species, while the small island of Porto Santo supplies an astonishing number, in general specifically distinct from those of Madeira, and the rocky islets called the Desertas, with difficulty accessible by man, have each some peculiar forms and in great abundance.

These facts seem to indicate that Great Britain and Ireland, including the Hebrides, Orkney, Zetland Islands, &c., have at one time formed part of the European continent, but that the more distant islands which I have named-raised by volcanic action from the depths of the Atlantic, have been each the scene of the creation of certain species which have been confined within their narrow limits by the surrounding sea.

Opposed to this idea is the fact already alluded to, that some marine littoral species, I may particularly mention Littorina striata, are common to West Africa, the Canaries, Madeira, and the Azores, which (as it is quite impossible for littoral phytophagous animals to have travelled

along the bottom of the ocean,) would lead us to infer that the African continent had at one time extended as far west as the last-named islands, in accordance with an opinion very ably supported by Professor Edward Forbes, in his report on the connexion between the distribution of the existing Fauna and Flora of the British Isles, published in the memoirs of the Geographical Survey of Great Britain. Which of these theories is correct, or whether they can both, with some modification, be reconciled to each other, I must leave for geologists to determine. The only solution which suggests itself to me is, that the shores of the African continent may have extended as far west as the islands in question, and that immediately on the subsidence of the land, when it was barely submerged, and the conditions not yet incompatible with the existence of littoral speeies of marine Mollusca, the volcanic action took place, elevating the lofty masses of which most of these islands are composed, and that their peculiar land mollusca are of more recent origin.

Snch an explanation would, I believe, be consistent with established geological facts, but I merely suggest it for the consideration of those who are more qualified than I can pretend to be to grapple with the vast subject of the history and conditions of our planet, in times anterior to the present distribution of land and water.

THIRD MEETING.

ROYAL INSTITUTION.-November 14, 1853.

JOSEPH DICKINSON, M.D., F.L.S., &c., PRESIDENT, in the Chair.

At an EXTRAORDINARY MEETING, held previous to the Ordinary Meeting, the following resolution, passed at the last Extraordinary Meeting, was read and confirmed, viz.-"That the Subscription, payable by Ordinary Members, be increased to £1 1s. Od. for the present session."

It was moved by Mr. JOHN FORSHAW, and seconded by the Rev. Dr. HUME: "That this Society appoint five members of Council, viz.— The Treasurer and Secretary, Mr. J. P. G. SMITH, Dr. W. IHNE, and

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