[ 469 ] XIV. Report on the Hijdroida collected dtiring the Expeditions of H. M.S. '■Porcupine.' By Professor G. J. Allman, F.B.S. Eead ISth February, 1873. [Plates LXV. to LXVIIL] J. HE Hydroids obtained during the two expeditions of the 'Porcupine' (1869 and 1870), and placed in my hands for determination, consist of trophosomes, in some cases destitute of gonosome, but in others provided with this important element of the colony. No free planoblasts are contained in the collections of either expedition. The dredgings of 18G9 are, on the whole, from greater depths, and contain a greater number of new species than those of 1870 ; for though a few of the specimens of the expedition of 1869 are from inconsiderable depths (64, 75, and 90 fathoms), the majority are from very deep water, having been dredged from depths varying from upwards of 100 to between 600 and 700 fathoms. The deepest dredgings of 1870 were from 539 fathoms. One result of the expeditions has been the determination of the very extensive range of depth enjoyed by some well-known species. Thus Sertularella polyzonias, though very generally distributed in the zone between tide-marks, was brought up by the 'Porcupine' explorers from a depth of 374 fathoms. Ilydrallmania falcata, though a common species on the European shores of the Atlantic in the coralline zone of Forbes, which corresponds to a depth of between 15 and 50 fathoms, was obtained by the ' Porcupine ' explorers from a depth of 542 fathoms ; while Thuiaria articulata was brought up from 632 fathoms, though frequenting a depth of less than 50 fathoms round our shores. Many species which, have not yet been obtained elsewhere were brought up from great depths. Among these is a Diphasia from a depth of 632 fathoms; while a Plumularidan which must be referred to a new genus {Cladocarpus) was brought up by the same haul of the dredge. Two new species of Thuiaria were dredged from a depth of 640 fathoms, and a Lafoea from 345 fathoms. A Sertularella nearly allied to S. Gayi, of which it may, perhaps, be regarded as only a variety, ranged from 290 to 605 fathoms. It is a fact by no means without significance, that, in every case hitherto observed, these deep-water Hydroids belong to forms which produce fixed sporosacs instead of planoblasts. In the records of the expedition of 1869, it is stated that fragments of a Hydroid were VOL. VIII. — PART VIII. April, 1874. 3 u
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