NARRATIVE OF THE CRUISE. '277 



will bust be done by briefly pointing out the peculiarities in the external and internal 

 organisation of the Elasipoda. The shallow water Holothurians have not been at all 

 overlooked, for a large collection of such forms was brought home from different localities ; 

 but these Holothurians, being mostly already known, are not of sufficient interest to 

 deserve mention here. However, to give an idea of what the Challenger Expedition has 

 done with regard to the shallow water forms, it may be noted that a great number of 

 new species has been dredged, previously known species have been found in many new 

 localities, and several interesting biological observations made. 



" Only three Elasipoda were previously known, viz., Elpidia glacialis, Kolga hyalina, 

 and Irpa abyssicola, all obtained from the North Atlantic Ocean and the Arctic Sea; but 

 the Challenger Expedition has so far extended our knowledge of this peculiar group of 

 animals, that no less than fifty-two species and three varieties, divided into nineteen genera, 

 have been described. 1 Only eight of these species were found at depths less than 1000 

 fathoms — not a single one from a depth less than 50 fathoms — the remainder being 



Pia, 110.— Peniagone wyvillii, Thee]. 



obtained from depths exceeding 1000 fathoms. The greatest depth at which any living 

 Holothurid has been obtained is 2900 fathoms. The Elasipoda are distributed through- 

 out all seas, especially Oneirophanta mutabilis, which is almost cosmopolitan. Therefore 

 there seems to be every reason for the opinion that the Elasipoda are highly characteristic 

 of the deep-sea fauna, for, as above pointed out, this order is almost unrepresented in 

 the shallow water fauna, and, besides, presents forms perhaps the most aberrant met 

 with in any group of deep-sea animals. With regard to their geographical distribu- 

 tion, the peculiar fact maybe noted that some species are obtained from very distant 

 localities. Thus, for instance, Elpidia glacialis occurs in the North Atlantic Ocean 

 and the Arctic Sea, but was also obtained by the Challenger Expedition at Station 

 160, south of Australia, and Latmogone violacea was first dredged by the same Expedition 

 close to Sydney, and lately it has been found in great abundance by the 'Knight 

 Errant,' between the Faeroe Islands and the coast of Scotland. 



"Thus the Elasipoda represent the deep-sea forms among the Holothurioidea, while 



1 Zool. ChalL Exp, part xiii., 1881. 



