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Show 1882.] MR. S. O. RIDLEY ON THE CORALLIID^E. 221 Atlantic. The Amphihelia are found in the North Atlantic and Florida seas, besides off Madeira; but Cladocora debilis appears to be a local species. The Balanophyllia is new, and has no definite alliances. Ceratotrochus johnsoni is a remarkable form of a genus of very great distribution; and Caryophyllia endothecata is so important a coral that I shall venture to write a separate memoir about its bearings on classification. EXPLANATION OP PLATE VIII. Fig. 1. Caryophyllia endothecata, p. 216, natural size. 2. , the calice, magnified, 3. , interseptal loculi, magnified. 4. , costaj, magnified. 5. Ceratotrochus johnsoni, p. 217, natural size. 6. , a second specimen, natural size. 7. • , the calice, magnified. 8. , the costa?, magnified. 9. Balanophyllia brevis, p. 219, natural size. 10. , magnified. 11- , calice, magnified. 12. , diagram of the septal arrangement. On the Arrangement of the Coralliida, with Descriptions of new or rare Species. By STUART O. RIDLEY, M.A., F.L.S., &c, Assistant in the Zoological Department, British Museum. (Communicated by Dr. GCTNTHER V.P.Z.S.) [Received January 23, 1882.] (Plate IX.) The small group of species which has been thought worthy of separation from the rest of its Alcyonarian allies as a distinct family under the name Coralhda (more correctly Coralliida), is chiefly remarkable in its structural characters for possessing a continuous stony axis, covered by only a thin cortical layer of a softer spiculi-ferous material, into which the polypes are retractile. Its best claim to general notice lies in the fact that the Precious Coral of commerce (Corallium rubrum, Costa, rectius nobile, Pallas) is one of the only three species hitherto known to exist in the seas of the present time which have been included in it. The other two species are scarcely known, even to students of the group. Thus but one specimen of the species described by Dana (U. S. Expl. Exped., vol. vii. p. 641 pl lx fig. 1) under the name of Corallium secundum seems to have ever been described ; and but one specimen of the third species described by the late Dr. Gray (P. Z. S. 1860, p. 393, Rad. pl. xviii.) u n d e r the name of Corallium (subsequently altered to Hemicorallium) johnsoni, was obtained in the first instance, and I know of no other authentic specimen. The original specimen of this species however, is fortunately preserved in the national collection; that of |