340 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



On August 7th there is a well-marked increase upwards, 

 so that most of the plankton comes to be in the zone 

 10-0 faths. Finally, on August 10th, with the exception 

 of the Diatoms, there is again an increase upwards, and 

 most of the organisms are, as in most other cases, in the 

 top 10 faths. This supports the conclusion we arrived at 

 in the first part of this Report ('08, p. 130), that the most 

 populous zone in the Irish Sea is below the surface but 

 above 10 faths., and is in some cases between 5 and 10 

 faths. 



Limitations of Vertical Hauls. 



Beyond the above general conclusions as to the 

 average catch, and as to the proportionate representation 

 of the chief groups in the different seasons and zones of 

 depth, we do not consider it possible to go. For the 

 purpose of testing the reliability of the evidence given by 

 the vertical closing nets in regard to further details, viz., 

 the numbers and distribution of species, we have, in the 

 first instance, made a careful examination of certain pairs 

 of hauls made through the same distance, in exactly the 

 same way, at the same spot and within a few minutes of 

 each other. During the three years 14 such double hauls 

 have been made. In no case did the two nets contain 

 exactly the same species, in one case as many as ten 

 species present in one haul being unrepresented in the 

 other. This was on August 7th, '09, in mid-channel, 

 about 13 miles from land, the net being the Xansen 

 hauled from 20 to 10 faths. The species were: — 

 ChcEtoceros teres, C. criophilum,, Coscinodiscus radiatus, 

 Rhizosolenia shrubsolei, Ceratium fusus, C. tripos, Peri- 

 dinium sp., larval Polychata, Acartia clausi, and Micro- 

 cat anus yusillus. 



