DISTRIBUTION IN SPACE. 165 



Iiaving brouglit up fragments of a li3(lr()i(l from a depth of 2 135 fathoms, tlic greatest at wliieh 

 dredging has ever been accomplished.' 



Even single species of hydrnids arc distinguished by the great extent of their bathymetrical 

 range. Thus SerlidnrcUa j)oIj/~oiiia.s; a species also remarkable for its very wide horizontal area, 

 ranges in vertical distribution from a zone between tide-marks to a dejjth of 374 fathoms, from 

 which specimens were brought up during the expedition of the " Porcupine." llydraUmania 

 falcata was obtained during the same expedition from a depth of 542 fathoms, though it is a 

 common species in the " Coralline zone" of Forbes, which corresponds to a depth of between fifteen 

 and fifty fathoms, while T/miaria articulata M'as brought up from G32 fathoms, though frequenting 

 a depth of less than fifty fathoms round our shores. 



Many species which have not yet been obtained elsewhere were brought up from great 

 depths by the dredges of the "Porcupine." Among these is a Dijjhasia from a depth of G32 

 fathoms, while a plumularidan, which must be referred to a new geiuis, was brought up by the 

 same haul of the dredge. Two new sj)ecies of T/iuiaria were dredged from a depth of 640 fathoms, 

 and a Lafoea from 345 fathoms. A Sertularella, nearly allied to 8. Gayii, 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 interest, that in every case hitherto observed, these deep-water hydroids belong to forms 

 which produce fixed sporosacs instead of planoblasts.^ 



The cold area lying between Shetland and the Faroe Isles, which is overflowed by a deep icy 

 current from the polar seas, and whose discovery by the " Porcupine" explorers constitutes one 

 of the most important additions to our knowledge of the physical geography of the North Atlantic, 

 is not without a deep sea hydroid fauna, although its bottom varies from the freezing point of 

 freshwater to nearly two and a half degrees of Fahrenheit below it. Tlie two new species of 

 Thuiaria already alluded to were olitained from it where the temperature of the bottom is as 

 low as 30° Fahr., while from the same area the new plumularian genus, with the new species of 

 Diphasia and Lafoiki, also referred to above, were obtained in water whose temperature varied in 

 different places from 30°-5 Fahr. to 29°-S Fahr.' 



' The record of this fact is contained in the Report of the " Porcupine" Expedition, where, from a 

 depth of 2435 fathoms, in lat. 47° 38' N., long. 12° 08' W., the dredge is stated to have brought up 

 " two fragments of a hydroid zoophyte." (" Preliminary Report of the Scientific Exploration of the Deep 

 Sea in H.M. Surveying Vessel ' Porcupine,' during the Summer of 1869." — ' Proc. Roy. Soc.,' Nov., 

 1S69, p. 429.) The specimens seem unfortunately to have been lost, so that no special determination 

 of the hydroid obtained from this great depth has been possible. 



" A special report, which I have prepared on the hydroids collected during the expedition of the 

 " Porcupine," will appear in the general Report of the Expedition. 



^ In connection with deep dredging we must here refer to the researches of Sars, who, before the 

 English exploration of the deep sea was undertaken, dredged round the Scandinavian shores in depths 

 which, however, never exceeded 450 fathoms. In these dredgings he obtained, from a depth of 300 

 fathoms, two hydroids, Campanularia verticellaia, Linn., and a new genus and species, Lafocina tenuis, 

 Sars. (See Sars in " Yidenskabs-Selskabs Forhandlinger," for 1868, p. 246. Translated in 'Ann. 

 Nat. Hist.' for June, 1869, p. 423.) 



The late exploration of the Gulf Stream, undertaken by the United States Coast Survey, must 

 also be referred to. In this expedition very important additions were made to our knowledge of the 

 fauna of the sea bottom in the western part of the Gulf Stream, though no dredgings which can be 



