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Show 794 PROF. J. R. GREENE ON A RARE MEDUSA. [Dec 10, the only charybdeid which has been reinvestigated by several observers. In particular Claus has just given us a monograph describing and illustrating, with great minuteness of detail, the form and structure of this common Mediterranean Medusa. His essay may justly rank as the most thorough analysis, hitherto published, of the anatomy of any Medusa whatsoever. The affinity here noted was perceived by Fritz Muller, who at once referred his Medusae to Gegenbaur's Charybdeidee, in the definition of which family he proposed some modifications, to adapt it for the reception of the two species of the new genus Tamoya. The characters of the latter he contrasted with those of Charybdea (=C. marsupi-alis only) in parallel columns. But writing in 1859, at a distance from Europe, Fritz Muller needed the data we now possess for such a comparison. Claus, with his better knowledge of the Mediterranean species, has shown that the differences on which his predecessor relied do not in fact exist. W e cannot estimate as of generic value the characters which separate C. marsupialis from T. haplonema. These Medusae are therefore now placed in one genus (Charybdea of Claus, not Peron and Lesueur). They are very like one another, though both are obviously distinct from the rarer Brazilian species, T. quadrumana, for which the genus founded by Fritz Muller may still be retained. The Brazilian is indeed much larger than the Mediterranean Charybdea, and in this respect resembles one of the unnamed Charybdeidee (from the Philippine seas) provisionally described and figured in outline by Semper, who doubts the specific identity of any of his own forms with either of those discovered by Fritz Muller. The Charybdeidee are, unquestionably, of the greatest interest to any person wishing to understand the classificatiou of the Hydrozoa. They occupy an intermediate position between the lower and the higher Medusae, although, arbitrarily, they may be placed with the latter. Their (1) external morphology, (2) curiously modified ccelenteric system, (3) genitalia quite distinct from the central region of the bell, with its four accessory cavities for the gastric tentacles, (4) muscular apparatus, and (5), above all, their very distinct nervous ring and wonderfully complicated sensory organs display a number of characters, the study of which must amply reward every earnest student of the lower animals. The whole of this subject, to which, sixteen years ago, I endeavoured to direct attention, is now, at length, admirably presented in the work of Claus. No English zoologist has written on the Charybdeidee ; nor, so far as I am aware, has any paper on the Medusae been read before our Society since Edward Forbes, in 1851, made a communication on AEquorea. But the study of the Charybdeidee is so important that I have thought it desirable to append to the present note a brief history of the literature of these animals. Plancus (1739) was the first to describe and figure one of the Charybdeidee. His "urtica soluta marsupium referens" is tbe |