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Show 1896.] OF THE GENUS SERGESTES. 937 Several years ago, when trying to determine the very rich material of pelagic forms (among them also the type specimens of the 15 species described by Krdyer) preserved in the Zoological Museum of the University in Copenhagen, I discovered the value of numerous species, but 1 had no mind to write any preliminary note on the question. Since then I have not had the time necessary for working out a monograph (requiring some hundred figures); but seeing now that at least during some years I shall be very much engaged with other work, while authors continue to describe larvae as well-established new species, I have thought it convenient to write this communication. A monograph will, nevertheless, be extremely desirable, for of most species and larval stages new full, and accurate descriptions and new figures, much better than the existing ones, must be worked out. Many of the described forms it is impossible to recognize with certainty without a re-examination of the type specimens. A monograph must also be based upon the investigation of the collections in the few museums which possess rich material of pelagic Crustacea; it will be rather toilsome, but very remunerative, as at the present time it is scarcely possible within any other group of Decapoda to elucidate a large portion of the development of almost two-thirds of the species. The genus Sergestes is now generally referred to a separate family, the Sergestidce. To this also the following genera have been transferred|: Sciacaris, Bate ; Petalldlum, Bate: Acetes, H . M.-Edw.; and Leucifer, Vaugh. Thomps. On Sciacaris and Petalldlum some remarks will be communicated in the following pages; the two other genera I must omit on this occasion, though much addition to our knowledge could be given. Leucifer has been treated at great length by Bate, who admits only 2 species, but 4 species are preserved in our museums. Of Acetes 2 species are known (one of which has not been examined since 1837), but we possess 6 species, tbe distinctive characters of which are very curious ; it is, however, impossible to give a good idea of the species of these two genera without a considerable number of figures. Before concluding these few remarks I desire to offer m y sincere thanks to Prof. Dr. K. Brandt (Kiel) and Geheimrath Prof. Dr. R. Leuckart (Leipzig), w ho lent m e two type specimens, and especially to Geheimrath Prof. Dr. V. Hensen (Kiel), who lent me examples of 4 Plankton species, aud Prof. Dr. C. Chun (Breslau), who, ou m y request for the loan of type specimens of two species, favoured m e with his whole finely preserved material collected by himself, chiefly with a closure-net, " Schliessnetz," at the Canary Islands and at Ragusa and Lesina in the Adriatic. ii. The History of the Genus. As C. Spence Bate and A. Ortraann, the last two authors who have given an apparently but not really complete enumeration of the known species, have overlooked several publications, and as |
