1898.] PLANKTON OF THE FAEROE CHANNEL. 547 



value, occurred rarely (C, hyperboreus) ; one, Pseudocalanus elon- 

 gatus, is only represented three times, and cannot therefore be 

 further discussed; two, Metridia longa Lubbock (= armata 

 Boeck) and Euchaeta norvegica, are well represented. Both of 

 these species exhibit, in the table of percentages above given, that 

 preference for a mesoplanktonic existence which one would expect 

 of an Arctic species in a Frontier district. For if the law be true, 

 which was enunciated first, I think, by Moebius, that the area of 

 distribution of a Planktonic organism is bounded at the surface by 

 an isotherm and below by an isothermobath of the same number 

 of degrees, we should expect Arctic forms to sink to lower (colder) 

 depths as they approached lower latitudes (warmer surface-water). 

 The southernmost points recorded in Griesbrecht's lists for these 

 two species at the surface are the northern part of the North 

 Sea for Euchceta norvegica, and Concarneau for Metridia longa. 

 We are probably safe in assigning a maximum mean annual tem- 

 perature * of 50 F. for Metridia longa, and a slightly lower mean 

 annual for Euchceta norvegica. In the very interesting collections 

 made by Prof. Herdman in his traverse of the North Atlantic 2 , 

 the eight captures of ^Metridia longa were all near the mean annual 

 isotherm of 50 F. ; Euchceta norvegica was not captured at all. As 

 regards the vertical distribution of Euchceta norvegica, the Norwegian 

 North Atlantic Expedition failed to capture this species at tbe sur- 

 face 3 , but it certainly comes to the surface in the Faeroe Channel, 

 even in broad daylight (Sta. lie). 



The other two forms, which, according to the table of per- 

 centages given above, exhibit an apparent preference f or the Meso- 

 plankton Eucalanus attenuatus and Pleuromma abdominale, 

 are united in having a very wide superficial range in the Atlantic 

 and Pacific Oceans ; both occur in Griesbrecht's list of mesoplank- 

 tonic Copepoda, Eucalanus attenuatus being credited with 1000 m. 

 = + 550 fms., Pleuromma abdominale with 4000 m.= +2200 fms. 

 Both these species must be regarded as eurythermal and eurybathic ; 

 and it is not at present possible to suggest a maximum or minimum 

 temperature for either of them. Their apparent preference for 

 the Mesoplankton in my collections must therefore be attributed 

 to some other cause than temperature ; but it is in no way incon- 

 sistent with what we already know of their habits. 



Temora longicornis appears to be confined to the North Atlantic, 

 except for two records from the Mediterranean which Griesbrecht 

 appears to doubt 4 . So far as I am aware, it has never been 

 recorded from any considerable depth, and with this my results 

 accord : we may fairly regard it as a member of the Epiplankton ; 



1 The mean annual temperatures are adopted from Buchan, Ohall. Rep. 

 Phys. Chem. ii. Atmospheric Circulation. 



2 W. A. Herdman, I. C. Thompson, and A. Scott: Trans. Liverpool Biol. 

 Soc. xii. 33. 



3 G-. O. Sars: Crustacea of the Norwegian N. Atlantic Expedition, i. p. 240. 



4 W. Giesbrecht, op. cit. pp. 328-330. Mr. Thompson informs me by letter 

 that this species occurs also in a collection made at Muscat by Staff-Surgeon 

 Bassett-Smith, E.N., of H.M.S. 'Cossack.' 



