FAM. HYDROLARIDAE.—This family contains the remarkable genus _Lar_, which was discovered by Gosse attached to the margin of the tubes of the marine Polychaete worm _Sabella_. The zooids have only two tentacles, and exhibit during life curious bowing and bending movements which have been compared with the exercises of a gymnast. The Medusae (Fig. 132, A and B) have been known for a long time by the name _Willsia_, but their life-history has only recently been worked out by Browne.[310] {274}FAM. MONOBRACHIIDAE.—_Monobrachium_, found in the White Sea by Mereschkowsky, forms a creeping stolon on the shells of _Tellina_. The zooids of the hydrosome have only one tentacle. FAM. MYRIOTHELIDAE.—This family contains the single genus _Myriothela_. The zooid of the hydrosome stage is solitary and is provided, as in the Corynidae, with numerous scattered capitate tentacles. The gonophores are borne by blastostyles situated above the region of the tentacles. In addition to these blastostyles producing gonophores there are, in _M. phrygia_, supplementary blastostyles which capture the eggs as they escape from the gonophores and hold them until the time when the larva is ready to escape. They were called "claspers" by Allman. In some of the Arctic species Frl. Bonnevie[311] has shown that they are absent. Each zooid of _M. phrygia_ is hermaphrodite. [Illustration: FIG. 134.—_Pelagohydra mirabilis._ _Fl_, The float; _M_, position of the mouth; _Ten.Fl_, filamentous tentacles of the float. (After Dendy.)] FAM. PELAGOHYDRIDAE.—This family was constituted by Dendy[312] for the reception of _Pelagohydra mirabilis_, a remarkable new species discovered by him on the east coast of the South Island of New Zealand. The hydrosome is solitary and free-swimming, the proximal portion of the body being modified to form a float, the distal portion forming a flexible proboscis terminated by the mouth and a group of scattered manubrial tentacles. The tentacles are filiform and scattered over the surface of the float. Medusae are developed on stolons between the tentacles of the float. They have tentacles arranged in four radial groups of five each, at the margin of the umbrella. As pointed out by Hartlaub,[313] _Pelagohydra_ is not the only genus in which the hydrosome floats. Three species of the genus _Margelopsis_ have been found that have pelagic habits, and two {275}of them have been shown to produce numerous free-swimming Medusae by gemmation; but at present there is no reason to suppose that in these forms there is any extensive modification of the aboral extremity of the zooid to form such a highly specialised organ as the float of _Pelagohydra_. The affinities of _Pelagohydra_ are not clear, as our knowledge of the characters of the Medusa is imperfect; but according to Dendy it is most closely related to the Corymorphidae. _Margelopsis_ belongs to the Bougainvilliidae. ORDER IV. CALYPTOBLASTEA—LEPTOMEDUSAE.