■1 THE VOYAGE OF H.M.S. CHALLENGED 



This discovery was the introduction to the knowledge of the order Eksipoda. The 

 Norwegian Atlantic Dredging Expeditions, from 1876-1878, also brought home from 

 the extreme depths of the North Atlantic two curious forms, Irpa 1 and Kolga, 2 which 

 have been most carefully described by Danielssen and Koren, and considered by them as 

 belonging to the same family as Elpidia. 



The obscurity which involved the abyssal fauna was first fully dispelled by the 

 dredgings during the Challenger expedition ; and honour is due to its scientific staff, 

 but above all to its director, Sir C. Wyville Thomson, F.R.S., for having brought to 

 light numerous forms hitherto unimagined, equally surprising in outer form and inner 

 organisation. While hitherto only three Elasipoda were known, this report contains 

 descriptions of no less than fifty-two species and three varieties, divided into nineteen 

 genera. Besides the three forms before mentioned, sixteen were described in the Pre- 

 liminary Report on the Holothuridse of H.M.S. Challenger. 3 



The Elasipoda are true deep-water forms, and they may with all the more reason 

 be said to characterise the abyssal fauna, as no single representative, as far as at present 

 known, has been found to exist at a depth less than 50 fathoms. Only one form, viz., 

 Elpidia glacialis, Theel, has been dredged at this inconsiderable depth ; but then I 

 would point out that this was found in the Arctic Ocean, where it may be supposed that 

 deep-sea forms are able to live at a comparatively trifling depth. Elpidia glacialis, 

 Theel, at the same time appears to be a true abyssal form, and capable of existing at 

 a great variety of depths. One specimen was, for instance, found living at a depth of 

 900 fathoms near the coast of Greenland, and a great number of individuals were 

 dredged during the Norwegian Expeditions in the North Atlantic, at considerable 

 depths ; and finally, the Challenger Expedition brought home an individual dredged 

 from Station 160, at a depth of 2600 fathoms. 



A glance at the list given below will show that four species only are found at depths 

 varying from 50 to 500 fathoms, and as many from 500 to 1000 fathoms, but that all 

 the rest are obtained from dredgings exceeding 1000 fathoms. Thus we learn that the 

 Elasipoda abound over the floor of the ocean at great depths, and that the number of 

 species and of individuals is greatly reduced shorewards. The greatest depth at which 

 any living Holothurid has been obtained is 2900 fathoms. 



1 Echinodenner fra den Norske Nordhavsexpedition. Nyt Magazin for Naturvidenskaberne, 24-de Binds 3 Hefte, 

 Christiania, 1877. 



2 Echinodenner fra den Norske Nordhavsexpedition. Nyt Magazin for Naturvidenskaberne, 25-de Binds 2-det 

 Hefte, Christiania, 1879. 



3 Bihang till Kongl. Svenska Vet. Akad. Handlingar, Band 5, No. 19, Stockholm, 1879. 



