452 THE VOYAGE OF H.M.S. CHALLENGER. 



occurs in a smaller collection of Hexactincllida dredged by Dr. Hilgendorf at the 

 same locality, and also graciously placed at my disposal. Of course one cannot conclude 

 from this single instance that at all the localities explored on the Challenger Expedition, 

 eight times as many species would have rewarded a more prolonged exploration, but the 

 facts above communicated are calculated at least to convey an impression of the relatively 

 small proportion of the really existing Hexactinellid species that rewarded the search of an 

 expedition so splendidly equipped and successfully conducted as that of the Challenger. 

 And if one further considers that in spite of the large number (276) of dredgings or 

 trawlings undertaken, immense marine regions, especially the North Arctic and the 

 greater part of the Indian Ocean, were hardly touched upon, and that in many of the 

 regions traversed only sample searches were made, one cannot avoid the conviction that, 

 in spite of the relatively important increase of knowledge obtained by results of the 

 Challenger Expedition, only a small percentage of the really existing Hexactinellid 

 species have as yet been discovered. 



