546 BE. G. H. FOWLER ON THE [June 21 , 



cji-tainly tiuished below the 100 fathoms), in all 30 hauls, with 

 which to deal. Regarding, then, only those species which were 

 captured six times, or in 20 % of the hauls, as affording a suflBcient 

 basis for discussion, we find that the occurrences of seven spec-ies 

 work out thus, expressed in percentages of hauls made above and 

 below 100 fathoms : — 



Epiplankton. Mesoplankton. 



Calanus finmarchicus 88-2 "/o 1000 7o 



Eucalanus attenuatus 17'6 „ 46'1 „ 



KuchcEta norvegica 11'7 „ 76'9 „ 



Metridia longa 23-5,, 69-2,, 



Pleuronima abdominale 5'8 „ 61'1 „ 



Acartia clausii 35'2 ,, 15'3 ,, 



Temora longicornis 35'2 „ O'O „ 



From this table it would appear (1) that Calanus finmarchicus is 

 essentially eurythermal and eurybathic, i. e. has a wide range both 

 of temperature and of depth ; (2) that Eucalanus attenuatus, 

 Euchceta norvegica, Metridia longa, and Pleuronima abdominale show 

 a distinct preference for the deep water and low temperature of 

 the Mesoplankton, although occurring more sparingly in the 

 Epiplankton; (3) that Acartia clausii belongs rather to the 

 Epiplankton than to the Mesoplankton ; (4) that Temora longicornis 

 is essentially a member of the Epiplankton. We may now com- 

 pare these results, based unfortunately on but scanty data, with 

 those recorded by others. 



In the first place, Calanus finmarchicus, as mentioned above, 

 has been recorded from most varied temperatures (latitudes), and 

 is now definitely shown to extend to considerable depths (Sta. 18 h, 

 530-400 fm.). It does not occur among the Mesoplanktouic forms 

 in Giesbrecht's list (ojj. cit. p. 788), and its vertical distribution in 

 the Faeroe Channel is therefore worth recording. It is not at 

 present safe to suggest a maximum temperature, as expressed 

 by mean annual isotherms, for this species ; it is, however, possible 

 that its non-occurrence in the Equatorial region may indicate a 

 maximum of 75° or 80° F. as its temperature Umit. 



In the second place, it is noteworthy that of the five species of 

 Copepoda recognized by Chun ^ as essentially Arctic types (Leit- 

 formen), one is missing from the ' Research ' collections (Calanus 

 cristatus) ; one, regarded by Mr. Thompson as a species of doubtful 



the bottom than with the Mesopliuikton ; (2) the Mesobeiitlios, which seems on 

 statistical and otbei- grounds to have cerhain marked features, both faunistic 

 and physical, v.hicb distinguish it from the zones below and above it ; although 

 it shares many species with other zones, stiU, according to the ' Challenger ' results 

 (J. Murray, Summary of Scientific Eesults, Exped. H.M.S. Challenger, part ii. 

 p. 1430, table 1), no less than 74 per cent, of its fauna is confined to it, and 

 does not spread into other zones. 



These six words, with the addition of the terms " oceanic" and "neritic" as 

 applied respectively to the plankton of the open ocean and of the continental 

 region, have been found in practice to serve sufficiently well for descriptive 

 purposes. 



^ C. Chun, op. cit. p. 28. Hie list is a condensation from that of Q-iesbrecht, 

 op. cit. pp. 776-7. 



