Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/243

Rh species*. Alcide D'Orbigny† states that he has dredged Bryozoa at a depth of 160 metres off Cape Horn, and he considered the sea-bed there to be formed of dead and living Bryozoa. In many places the banks of Newfoundland are, in his opinion, covered entirely with similar debris, Cellepora‡ being especially abundant. The conditions most essential to the growth of Bryozoa, according to the same experienced observer, are:—first, considerable depth of water; secondly, clear and limpid water; thirdly, water constantly agitated by waves and deep currents. 13 out of the 26 British species found in the Coralline Crag belong to the genus Lepralia. According to Dr. Johnston§, the greater number of these species are found in deep water; and Mr. Busk mentions that the Lepralia ciliata has been dredged at 45, the L. Peachii at from 110 to 147, the L. hyalina at from 4 to 40, and the L. Malusii at 48 fathoms.

Amongst other common genera, of the Crag are Idmonea and Retepora, which may be considered essentially characteristic of rather deep seas. The Escharoe, again, live in deep water and among strong currents. One extinct species of this genus, the E. monilifera, is the abundant and characteristic species of the Coralline Crag. Another common species is the Biflustra delicatula, now to be found only in the seas of Australia and Manilla. The curious globose genera Alveolaria and Fascicularia are extinct, and peculiar

of the Bryozoa collected in the Mediterranean in the late voyage of the ' Porcu- pine,' he believes that R. Beaniana occurs in that sea. He has also furnished me with the following lists of Crag species now living in the Mediterranean and Adriatic, or fossil in the Italian Pliocene beds:—
 * Mr. Busk, however, has recently informed me that, from an examination

Crag species living in the Crag species occurring in the Mediterranean''. Italian Pliocene''.

Salicornaria sinuosa. Lepralia ansata. Lepralia annulata. "    Bowerbankiana. " ansata. "    Brongniartii. " Brongniartii. "    ciliata. " ciliata. "    innominata. " innominata. "    Malusii. " Malusii. "    mamillata. " Morrisiana? "    Morrisiana? " Pallasiana. "    Pallasiana. " unicornis. "    unicornis (tetragona, Reuss). " violacea. "    violacea. Retepora cellulosa.            Retepora cellulosa. Cupularia canariensis.         Cupularia canariensis. Patinella patina.              Membranipora andegavensis.                                   "      oceani. "     Lacroixii.                                Biflustra delicatula.                                Cellepora coronopus.                                   "      ramulosa. "     scruposa.                                   "      tubigera.

† Annales des Sciences Naturelles, 1851, p. 295.

‡ The curious Cellepora edax is often found covering, as a mantle, several species of univalve shells.

§ History of British Zoophytes. London, 1847.

VOL. XXVII.—PART I. K