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XIV. Report on the Hydroida collected during the Expeditions of H. M.S. ^Porcupine.' 



By Professor G. J. Allmax, F.R.S. 



Read 18th Pebmary, 1873. 



[Plates LXV. to T.XV1II.] 



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 1869 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-kno^Ti 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. Hydrallmania falcata, though a 

 common species on the European shores of ihe Atlantic in the coralline zone of Forbes, 

 which coiTesponds 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 682 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 Liphasia from a depth of 682 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 845 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 VIIL April, l^li. 3u 



