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Show ANNOTATIONS AND ADDITIONS. 275 nature who has added to his own many and valuable observations a comparison with those of others in all parts of the globe, Charles Darwin, places with greater certainty the depth of the region of living corals at 20 to 30 fathoms. (Darwin, Journal, 1845, p. 467; and the same writer's Structure of Coral Reefs, pp. 84- 87; and Sir Robert Schomburgk, Hist. of Barbadoes, 1848, p. 636.) This is also the depth at which Professor Edward Forbes found the greatest number of corals in the Egean Sea: it is his "fourth region" of marine animals, in his very ingenious memoir on the "Provinces of Depth," and the geographical distribution of Mollusca, at vertical distances from the surface. (Report on .lEgean Invertebrata, in the Report of the 13th Meeting of the British Association, held at Cork in 1843, pp. 151 and 161.) The depths at which corals live would seem, however, to be very different in different species, and especially in the more delicate ones which do not form such large masses. Sir James Ross, in his Antarctic Expedition, brought up corals with the sounding-lead from great depths, and entrusted them to Mr. Stokes and Professor Forbes for more thorough examination. On the west· of Victoria Land, near Coulman Island, in S. lat 72° 31', at a depth of 270 fathoms, Retepora cellulosa, a species of Hornera, and Prymnoa Rossii, were found quite fresh and living. Prymnoa Rossii is very analogous to a species found on the coast of Norway. (See Ross, Voyage of Discovery in the Southern and Antarctic Regions, vol. i. pp. 334 and 337.) In a similar manner in the high northern regions the whalers have brought up Umbellaria grrenlandica, living, from depths of 236 fathoms. (Ehrenberg, in the Abhandl. der Berl. Akad. aus dem J. 1832, s. 430.) We find similar relations of species and situation among sponges, which, indeed, are now considered to belong rather to plants than to zoophytes. On the coast of Asia Minor, the common sponge is found by those engaged in the fishery at depths varying from 5 to 30 fathoms; whereas a very small species of the same genus is not found at a less depth than 180 fathoms. (Forbes and Spratt, Travels in Lycia, 184 7, vol. ii. p. 124.) It is difficult to divine the reason which prevents l\ladrepores, Meandrina, Astrrea, and the entire group of tropical Phyto-corals which raise large cellular calcareous structures, from living in strata of water at a considerable depth |