1903.] PLANKTON OF THE FAEROE CHANNEL. 129 



Once it occurred in enormous quantity in St. Andrew's Bay in 

 company with Nyctiphanes norvegica, once at Redcar with a 

 similar swarm of Euthemisto compressa, the latter being also an 

 Arctic type-form l . In both these cases it is probable that the 

 creatures had been driven down the North Sea by a strong southerly 

 current, in the manner which I have already suggested 2 for 

 Parathemisto oblivia ; and it has therefore no more right to be 

 regarded as a " British " species than an occasional Velella or 

 lanthina brought up by the North Atlantic Drift to our shores. 

 According to Ortmann (op. cit.), the ' National ' hauls gave no 

 indication of the vertical distribution of this species. 



It will appear from the table (p. 119) that the ' Research ' was 

 more fortunate, and the hauls point to its having a distinct 

 preference for the mesoplankton in the Faeroe Channel. Like 

 (at any rate some) other mesoplanktonic species, it rises to the 

 surface at night. Specimens with adult characters were captured 

 in 1 9 per cent, of epiplankton hauls, but in 66 per cent, of meso- 

 plankton hauls. On the other hand, larval and post-larval stages, 

 apparently referable to this species, were obtained in 38 per cent, 

 of epiplankton hauls, but only in one mesoplankton haul, and 

 that one terminating near the 100 fathoms. The species, there- 

 fore, appears to be epiplanktonic when young, mesoplanktonic 

 when adult, so far as these observations go and in the Faeroe 

 Channel at this time of year. In seeking deeper (colder) water 

 in this locality, it follows what appears to be the practice of other 

 Arctic type-forms when they meet the warmer water of the North 

 Atlantic Drift. That this was not apparent from the results of 

 the ' National ' is probably due to the fact that f rom the Hebrides 

 almost up to the moment of coming into the Gulf -Stream the 

 vessel was in far colder surface-water than that of the Faeroe 

 Channel in summer. 



The larvae mentioned above ranged from an early Calyptopis 

 stage up to the adult condition. It was not, of course, possible to 

 derive them all with certainty from Thysanoessa longicaudata ; but 

 the majority may be safely referred to this species, not only 

 because the adults captured were far in excess of any other 

 Euphausid, but also because the larvae could be traced gradually 

 through successive stages back to the Calyptopis. The meta- 

 morphoses of this species follow the lines indicated by Sars 9 for 

 Nyctiphanes, Euphausia, and Thysanopoda. 



As Paul Mayer 4 has shown, the spination of the telson of 

 Malacostracan larvae yields a character important both for phylo- 

 geny and for diagnosis. It has not as yet, I think, been pointed 

 out that the condition of the telson in Euphausiidse affords a 

 further argument for the view maintained by Boas 5 and others, 



1 C. Chun : ' Beziehungen xwischen dem arktischen und antarktischen Plankton,' 

 Stuttgart, 1897, 8vo, p. 30. 



2 Proc. Zool. Soc. 1898, p. 583. 



3 G. O. Sars : Chall. Rep. Zool. xiii. (Schizopoda). 



4 P. Mayer : Jenaische Zeitschrift, xi. (1877), p. 246 et seqq. 



5 J. E. V. Boas : Morphologisches Jahrbuch, viii. p. 486. 



PROC. ZOOL. Soc. 1903, VOL. I. No. IX. 9 



