'imbricata, loricata, spinifera, daphnoides. 



300 DE. G. H. POWLEE — BISCAYAN PLANKTON : 



The Vertical Distribution oe Indivibtjal Species. 



f'" In'summary of the observations given aljove, it may be said that the species seem to 

 have^been distributed — at the date and in the area investigated — on the following lines : 



(a) Species confined to the epiplankton . . . haddoni, spinirostris, globosa. 



(6)ISpecies with a phirimum in the epiplankton,^ ^^^^^^ ^^^^ ^ \^r.^, procera, elegans, zetesios. 



but extending into the upper mesoplankton. J 

 (.) Species distributed as the last, and with their| ^^^.^^^^ rotundata, and perhaps hyalophyllum. 



oldest stage purely mesoplanktonic ... .J 

 (f/) Species extending into the lower epiplankton^ 



and with a (probable) plurimum in the upper 



mesoplankton, extending into the lower 



mesoplankton -' 



(e) Purely mesoplanktonic species ametru, brachyaskos, pusilla, rhynchena. 



To (<?) may probably be added kampta, tyloda, cucullata, pellucida ; to [b) castcmea. 



Those species Avhich occurred at any time in the epiplankton may be also classified as : 



, . , , ^ ^ „ f curia, haddoni, hyalophyllum, magna, A larvae, rotundata. 



Those which reached up to fm. -^ ' . . . , , ^ ^ 



^. spmirostris, globosa. 



„ ,, „ „ 25 „ daphnoides, elegawi. 



„ ,, „ J, 50 „ imbricata, loricata, spinifera, zetesios. 



„ „ „ „ 75 „ procera. 



It remains to be seen whether, as is possible, this relation is connected with 

 temperature barriers. 



It is interesting to note that of Miiller's new ' Valdivia ' species which were captured 

 by the ' Research,' ametra, brachyaskos, pusilla, kampta, rhynchena, and tyloda were purely 

 mesoplanktonic species ; and that " stigmatica " and " lophura " were apparently meso- 

 planktonic oldest stages of known epiplanktonic species. " Macrocheira " and 

 " etenophora " seemed to be similarly oldest stages of epiplanktonic species, but were 

 apparently themselves epiplanktonic. It is quite evident that the mesoplankton will be 

 far more productive of new forms than the epiplankton. 



Defijiitite Observations. 



I have employed this term elsewhere to denote those observations which show the 

 outside limits of depth, temperature, &c. between which a species has been captured ; 

 they are brought together in the first two main columns of the ensuing table under the 

 heads of " lowest possible " and " highest possible " depths and temperatures. To these 

 I have added — as the expression of a mere personal opinion — my own inferences as to 

 the real lower limits, under the heads of " lowest probable " depths and temperatures. 

 The third and fourth main columns recapitulate, for convenience of reference, the 

 oV/served plurima, and those general inferences as to distribution and oscillation, in the 

 area and during the period of the cruise, which have been drawn in the text. The 

 temperatures from 25-75 fathoms are unfortunately only approximations (see p. 5); 

 the others from the curve of observations made during the cruise. 



