Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/384

Rh In an essay 'On the Associations of Mollusca on the British Coasts, considered with reference to Pleistocene Geology,' printed in 1840, I described the mollusca as distributed on our shores and seas in four great zones or regions, severally denominated "the Littoral zone," "the region of Laminariæ," "the region of corallines," and "the region of corals." An extensive series of researches, chiefly conducted by the members of the committee appointed by the British Association to investigate the marine zoology of Britain by means of the dredge have not invalidated this classification, and the researches of Professor Löven in the Norwegian and Lapland Seas have borne out their correctness. The first two of the regions above mentioned had been previously noticed by Lamouroux, in his account of the distribution (vertically) of seaweeds; by Audouin and Milne Edwards, in their 'Observations on the Natural History of the Coast of France,' and by Sars in the preface to his 'Bagtivelser og Jagtivelser.' The Littoral distribution of mollusks has firequently attracted the attention of zoologists. An admirable essay on the fauna and flora of the Littoral and Laminarian zones on the coast of Denmark has recently been published by M. Oersted.

The first, or Littoral zone, is that tract which lies between the high and low water marks, and therefore is very variable in extent, depending for its dimensions on the amount of rise and fa11 of the tides. In all parts of the northern hemisphere it presents very similar phenomena when its animal and vegetable inhabitants are examined, whether it be only a few inches broad, as in the Mediterranean, or beyond 30 feet in vertical extent, as in some more tidal seas. Throughout Europe, wherever it consists of rocky it is characterized zoologically by species of Littorina, botanically by Corallina; where sandy, by the presence of certain species of Cardium, Tellina and Solen; where gravelly, by Mytilus; where muddy, by Lutraria and Pullastra.

In the British Seas its inhabitants vary in the northern and southern districts, but there are many species constant throughout, both of plants (as the species of the genera Fucus, Lichina, Laurencia and Corallina), and aninoals (as Littorina rudis, littorea and neritoides, Purpura lapillus, Patella vulgata, Cardium edule, Kellia rubra, and many Annellides and Zoophytes, never found out of this region). This zone is itself divisible into several distinct sub-regions as well defined by characteristic animals and plants where it is narrowest as where it is broadest. To show that this assertion of the constancy of even the sub-divisions of the littoral zone is not put forth vaguely, but from minute observation (which is equally true in regard to the statements respecting the other zones in depth), I append a table exhibiting the characteristic animals and plants