PROC. BIOL. SOC. WASH. 94(3), 1981, pp. 902-947 KEY TO THE GENERA OF OCTOCORALLIA EXCLUSIVE OF PENNATULACEA (COELENTERATA: ANTHOZOA), WITH DIAGNOSES OF NEW TAXA Frederick M. Bayer Abstract. — A serial key to the genera of Octocorallia exclusive of the Pennatulacea is presented. New taxa introduced are Olindagorgia, new genus for Pseudopterogorgia marcgravii Bayer; Nicaule, new genus for A^. crucifera, new species; and Lytreia, new genus for The sea plana Deich-mann. Ideogorgia is proposed as a replacement name for Dendrogorgia Simpson, 1910, not Duchassaing, 1870, and Helicogorgia for Hicksonella Simpson, December 1910, not Nutting, May 1910. A revised classification is provided. Introduction The key presented here was an essential outgrowth of work on a general revision of the octocoral fauna of the western part of the Atlantic Ocean. The far-reaching zoogeographical affinities of this fauna made it impossible in the course of this study to ignore genera from any part of the world, and it soon became clear that many of them require redefinition according to modern taxonomic standards. Therefore, the type-species of as many genera as possible have been examined, often on the basis of original type material, and a fully illustrated generic revision is in course of preparation as an essential first stage in the redescription of western Atlantic species. The key prepared to accompany this generic review has now reached a stage that would benefit from a broader and more objective testing under practical conditions than is possible in one laboratory. For this reason, and in order to make the results of this long-term study available, even in provisional form, not only to specialists but also to the growing number of ecologists, biochemists, and physiologists interested in octocorals, the key is now pre-sented in condensed form with minimal illustration. In using the key, it must be kept in mind that some common species have been repeatedly described under different names, and many others have been assigned to the wrong genera. The key cannot reconcile the generic identification reached for any given specimen with the existing literature. One cautionary example, perhaps a typical one, is the genus Heterogorgia. None of the species described in that genus by Nutting (1910) in his Siboga monograph will key out to the genus Heterogorgia, because most of them