LINNEAN SOCIETY OF LONDON. 27 



catch extending over the month, but not in exceptional catches, 

 are seen from this Hst to be in June and October, and especially 

 in the latter. 



If we look now for the largest individual hauls of a single 

 species of Copepod we find that they occur in April, August, 

 and September. The following are some of the more important 

 of these : — 



April 9— Pseudocalanus elongatus 16,000 



9 — Teinora longicoruis 19,000 



23 — Calanus belgolandicus 13,480 



24 — Acartia c] ausi 28,000 



Aug. 13-Oithouasimili.s 14,000 



17— „ „ 25,000 



24— Acartia clausi 29,000 



27— „ „ 24,700 



29 — Pseudocalanus elongatus 23,000 



Sept. 4 — Acartia clausi 23,600 



4 — Pseudocalanus elongatus 36,000 



12— „ „ 33,600 



18— „ ., 25,000 



20— Oitbona similis 29,270 



These also bear out the idea of maxima in April and in autumn, 

 the latter being the more important one ; in both cases they follow 

 the phytoplankton. As a rule a haul rich in Copepoda has few- 

 Diatoms, and vice versa, but the Copepoda do not, like the Diatoms, 

 present great maxima and marked depressions. Even when both 

 groups are present in the plankton we frequently find that they 

 are in different zones ; for exauiple, in some April hauls in 1907 

 the Diatoms were markedly on the surface and the Copepoda 

 below, while later in the year these positions were reversed. 



The distribution of particular Copepoda (Calanus, Anomalocera, 

 Microcalanns, Pseudocalanus, Centropages, Temora) have been fol- 

 lowed separately and form interesting studies. Calanus, Pseudo- 

 calanus, Centropages, and Temora are present throughout the year ; 

 Anomalocera appears in our district in spring ; Microcalanns in late 

 autumn. 



The Diatom fauna makes its appearance again in September 

 (fig. 3). The two surface-nets on Sept. 12th show very large 

 numbers of Diatoms, extending up to 13 millions and 16 millions 

 in single hauls in the case of Ehizosolenia semispina — in fact this 

 highest peak in the September maximum of Diatoms is mainly 

 composed of this one species of Bhizosolenia, whereas in the spring 

 maximum the bulk of the catch is made up of Chceioceros contortum 

 and Thalassiosira Nordenshioldii, species that are rare or altogether 

 absent in September gatherings. The genus Thalassiosira is 

 mainly a spring form, rarely present after May, and is not repre- 

 sented in autumn in this year's results. 



When a comparison is made between the three similar open 

 tow-nets which were worked together for 15 minutes at a time — 

 two at or close to the surface, and the other weighted so that it 

 was lowered to a depth of about ten fathoms, and gradually rose, 

 as the boat went slowly ahead, to a depth of a foot or two below 

 the surface — it is almost invai'iably found that the weighted net, 



