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Show 1896.] BRITISH HYDROIDS AND MEDUS.E. 491 two tentacles, with a single otolith in each. This specimen was taken off the Isle of Man. Another specimen, taken at Valencia, measured 20 m m . in width and 11 m m . in length, with 39 tentacles. One to three vesicles between every two tentacles, with a single otolith. Thirty-nine tentacles is the maximum number which I have counted in one specimen, and I have not seen more than three marginal vesicles between two tentacles. One or two vesicles are usually present between every tw-o tentacles in specimens possessing 30 to 35 tentacles, and one to three vesicles in specimens with more than 35 tentalces. The stomach is short, of a yellowish-brown colour ; and mouth with four lips. The generative organs occupy nearly the whole length of the lower or outer half of each radial canal, and terminate very close to the ring-canal. In mature specimens the generative organs hang in folds and are usually of a yellowish-brown colour. I have noticed in some specimens belonging to the intermediate stages that the generative organs have a greenish appearance, and occasionally the stomach and tentacles are greenish too. The greenish colour is not due to a green pigment, but to the reflection of light upon the organs. Many specimens 'taken at Valencia were infested with a species of Cercaria which lives in the mesoglcea. Hcdcampa usually selected this medusa, and was often seen attached to one of the generative organs, which showed a remarkable decrease in size compared with the others. PHIALIDIUM CYMBALOIDEUM (Van Beneden). (Plate XVII. figs. 1, 2, & 2 a.) Van Beneden first described this medusa in 1866 under the name of Thaumantias cymbaloides. I have changed the specific name from the Greek to Latin form, in accordance with the rules on nomenclature. This species has no connection whatever wdth Medusa cymbaloidea, Slabber, and the synonyms connected with it, which Haeckel has placed under the name of Epenthesis cymbaloidea. I first recognized this medusa during m y visit to Valencia in 1895, and was able to see many stages in development. As it often occurred along with Phialidium temporarium, I was able to compare the different stages. Van Beneden has not given a figure of the species, but his description is sufficiently good to recognize without doubt its identity with the medusae taken at Valencia. 1st Stage. Four tentacles. (Plate X V I I . fig. 1.)-Umbrella bell-shaped, about li m m . in length and about 1 m m . in width, wdth thick walls (thicker than in the corresponding stage of Phialidium temporarium). Four perradial tentacles, fairly long, and four interradial tentacle-bulbs. The basal bulbs of the tentacles and the tentacle-bulbs of a yellowish or reddish-brown colour. Eight adradial marginal vesicles, each with two or three otoliths. The |