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Show 1896.] BRITISH HYDROIDS AND MEDUS^l. 48l Banks to be unusually luminous, flashing in many parts like lightning. He directed some of the water to be hauled up, in which he discovered .... a large species of medusa, to which he gave the name pellucens. The Medusa pellucens measures about six inches across the crown or umbrella." This is clearly from the figure and description a Scyphomedusa. Shaw (1812) has copied the figure given by Macartney. Lesson (1843) has not only given Thaumantias hemisphcerica as a distinct species, but also Thaumantias lucida, Macartney. Amongst the synonyms of the latter Lesson has placed Medusa scintillans (=Noctiluca scintillans) and Medusa pellucens ( = Banks's Scyphomedusa), but in tbe description of the species he only gives Macartney's description of Medusa lucida. Haeckel apparently has copied from Lesson, without referring to the original papers, as he has placed as synonyms under Thaumantias hemisphcerica both Medusa scintillans and Medusa pellucens. Forbes (1848) next described Thaumantias hemisphcerica. It is first, however, important to consider Forbes's views upon the value of sense-organs or marginal vesicles for the identification of the species. Porbes, in 1841, gave the following advice on the identification oE species belonging to the genus Thaumantias:- " 1st. The number of tentacula (always a multiple of four). 2nd. The presence, absence, size, and colour of the eyes at their bases. 3rd. The colour of the cross-vessels and proboscis. 4th. The shape of the umbrella. 5th. The shapes of the clubs of the vessels. 6th. The form and lobation of the oral proboscis or peduncle. "I have mentioned these sources of character in what I conceive to be the order of their respective importance, but all should if possible be noted." I may here say that Forbes's statement that the tentacles are always a multiple of four is not correct. The multiple system is also adopted by Haeckel, and it leads to the assumption that Medusae have a most wonderful symmetry. The statement holds good up to thirty-two tentacles, but above that number the tentacles, when carefully counted, show odd as well as even numbers. I found, out of 47 mature specimens of Obelia lucifera, only two specimens showing an equal number of tentacles in each of the quadrants, and only nine specimens possessing a number that could be equally divided by four. Twenty-six specimens have an even number of tentacles, and 21 specimens an odd number. Forbes included in his genus Thaumantias several Medusae which have since been transferred to other genera, viz.:- Thaumantias pilosella ( = Euchilota pilosella). Thaumantias lucifera ( = Obelia lucifera). Thaumantias melanops ( = Tiaropsis multicirrata). All these have certain characteristic features by which they may PBOC ZOOL. Soc-1896, No. X X X I . 31 |
