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For, what we want is time, first, for the gradual formation, and then for the extinction of races and allied species, occasioning gaps between the survivors. In the year 1830 I announced, on the authority of M. Deshayes, that about one-fifth of the mollusca of the Falunian or Upper Miocene strata of Europe, belonged to living species.
In the last edition of Sir Charles Lyell's 'Elementary Geology' it is stated, on the authority of a former President of this Society, the late Daniel Sharpe, that between 30 and 40 per cent. of the species of Silurian Mollusca are common to both sides of the Atlantic.
But in parts of England, more especially in Yorkshire, Norfolk, and Suffolk, there are superficial formations of clay with glaciated boulders, and of sand and pebbles, containing occasional, though rare, patches of shells, in which the marine fauna begins to depart from that now inhabiting the neighbouring sea, and comprises some species of mollusca not yet known as living, as well as extinct varieties of others, entitling us to class them as Newer Pliocene, although belonging to the close of that period and chronologically on the verge of the later or Post-pliocene epoch.
Inferior tertiary strata, variation of, connected with volcanic action; Macrauchenia Patachonica at San Julian in Patagonia, age of, subsequent to living mollusca and to the erratic block period. SUMMARY. Area of Pampean formation. Theories of origin. Source of sediment. Estuary origin. Contemporaneous with existing mollusca. Relations to underlying tertiary strata.
There is no certainly known extinct order of Protozoa; there is but one among the Coelenterata that of the rugose corals; there is none among the Mollusca; there are three, the Cystidea, Blastoidea, and Edrioasterida, among the Echinoderms; and two, the Trilobita and Eurypterida, among the Crustacea; making altogether five for the great sub-kingdom of Annulosa.
Mr Banks also brought back many curious shells, and Mollusca; besides many species of coral, among which was that called the Tubipora musica. At six o'clock in the morning, we got under sail and stood away to the N.W., having two boats ahead to direct us; our soundings were very irregular, varying five or six fathom every cast, between ten and twenty-seven.
It is only, therefore, where there is a full representation of all the principal orders of mollusca, or when we compare those of corresponding grade, that we can fully rely on the percentage test, or on the proportion of Recent to extinct species as indicating the relation of two groups to the existing fauna.
In its most calcareous form the Mountain Limestone is destitute of land- plants, and is loaded with marine remains the greater part, indeed, of the rock being made up bodily of crinoids, corals, and bryozoa with interspersed mollusca. Palaeozoic type of lamelliferous cup-shaped Coral. Order ZOANTHARIA RUGOSA, Milne Edwards and Jules Haime. a.
But as we have been speaking so much of sea-creatures, I think we will now leave the oysters, cockles, mussels, and razor-fish, and choose the familiar garden-snail as our specimen of the Mollusca, or Soft-bodied Family. I fancy you need no introduction to that snug little householder.
We saw no land, not even an iceberg, and very few vessels. For five or six successive evenings when in the parallels of 40 and 41 degrees South between the meridians of 133 and 113 degrees West we enjoyed the fine sight of thousands of large Pyrosomae in the water, each producing a greater body of light than I ever saw given out by any other of the pelagic-luciferous mollusca or medusae.
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