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 0° 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 Feroe at the depth of 500 fathoms is from 0° to 
—1°C., 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 Ophioglypha stiwitzii, 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. 
From 800 to 2,000 fathoms all along the west coasts 
of Scotland, Ireland, and France, 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 Hehinus elegans, D. and K. ; 
Toxopneustes drobachiensis, O. F. MULLER; Brissopsis 
lyrifera, ForBES; Tripylus fragilis, D. and K.; the 
magnificent Brisinga coronata, G. O. Sars (Fig. 7), 
and B. endecacnemos, ABSJORNSEN ; Pteraster mili- 
taris, M. and T.; Ophiacantha spinulosa, M. and 7. ; 
Ophiocten sericewn, Forses ; Ophioglypha sarsii, 
LirK.; <Asteronyx lovéni, M. and T.; and Astero- 
