Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/387

374 this region, associated with such fiici as algologists usually deem inhabitants of deep water. A host of animals reside upon these algæ. Among mollusca, the genera Lacuna and Rissoa, the Patella pellucida and lævis, Pullastra perforans and vulgaris,and various Modiolæ are especially characteristic of this zone; and numerous zoophytes and Radiata especially Echinus sphæra, Tubularia, Actinea senilis, though ranging both higher and lower, are more prolific here than in any of the other regions. The coral-like Nullipora is the last and bounding plant of this zone in our seas, and rarely ranges with us below 20 fathoms at the utmost; though in more southern seas, as in the Mediterranean, it is found abundantly at depths as great as 70 and 80 fathoms, where, as here, it forms the out-post of marine vegetation in depth.

The third province in depth I have termed the Region of Corallines, for in it we find the greatest variety and abundance of the corneous zoophytes—arborescent animals, which seem here to take the place of plants. Here we find the great assemblage of carnivorous mollusca, the species of Fusus, Pleurotoma, and Buccinum. and many of the species of Trochus, Here too are most abundant the Naticæ, ,,Fissurellæ, Emarginulæ, Velutinæ, Capulus, Eulimæ, and Chemnitziæ, and among bivalves, Artemis, Venus, Astarte, Pecten, Lima, Arca, and Nucula, Numerous and peculiar Radiata, including the largest and most remarkable species, abound, and, for number, variety, and interest of the forms of animal life in the British Seas, this region transcends all the others. Its vertical range is from 15 to about 50 fathoms; its chief development between 25 and 35 fathoms.

The fourth and lowest of the regions of depth in the British Seas, I have termed the region of deep-sea corals. It is necessarily local as the greater extent of our marine area does not attain the depth at which this region commences, zoologically about 50 fathoms, or possibly considerably deeper. It has as yet been but very partially explored, but so far we know, is well characterized by the abundance of the stronger corals, the presence in quantity of species of the Dentalium-like genus of Annelides, called Ditrupa, by a few peculiar Mollusca, and by peculiar Echinodermata, as Astrophyton and Cidaris, and Amorphozoa, as Tethya cranium. All our British Brachiopoda inhabit this zone, and probably