CHAP. I.] INTRODUCTION. 43 



It seems probable that the distribution of marine 

 animals is determined by the extremes of temperature 

 rather than by the means. The mean winter tempera 

 ture of the surface and of moderate depths off the 

 north coast of Norway is about 2 C., and the extreme 

 about C. ; and on the coast of Greenland the mean 

 sinks to 1 C., and the extreme to 3 C. 



The temperature of the trough between Scotland 

 and Pyeroe at the depth of 500 fathoms is from to 

 1 C. 5 and we find in that trough, along with many 

 undescribed forms which are special to very deep 

 water, every one of the echinoderms hitherto found 

 on the coast of Scandinavia and Greenland, with the 

 single exception, I believe, of Opliioglyplia stuwitzii, a 

 shallow-water Greenland form among the ophiurids, 

 and of one or two holothurids which have as yet 

 evaded us. 



The temperature of the telegraphic plateau at 1,000 

 to 2,000 fathoms is apparently usually from 3 to 2 C., 

 and at 2,500 fathoms in the Bay of Biscay it is 2 C. 

 Prom 800 to 2,000 fathoms all along the west coasts 

 of Scotland, Ireland, and Prance, we have dredged 

 Scandinavian echinoderms in abundance, and from 

 the deep water as far south as the coast of Portugal 

 I have received examples of some of the best marked 

 northern forms, such as Echinus elegans, D. and K.; 

 Toxopneustes drobachiensis, O. P. MULLER ; Urissopsis 

 lyrifera, PORBES ; Tripylus fragilis, D. and K. ; the 

 magnificent Brisinga coronata, G. O. SARS (Pig. 7), 

 and IB. endecacnemos, ABSJOKNSEN; Pteraster mili- 

 taris, M. and T. ; Opliiacanlha spinulosa, M. and T.; 

 Ophiocten sericeum, PORBES ; Opliioglyplia sarsii, 

 LUTK. ; Asteronyx loveni, M. and T. ; and Astero- 



