LINNEAX SOCIETT OF LOXDOX. 35 



localities up to ten miles apart ; but on the other hand, even with 

 these same groups there may, on other dates, be very diverse hauls 

 indicating an uneven distribution. Some species, and some groups 

 of neritic larvae markedly congregate in shoals, and this also adds 

 to the uneveuness of the distribution. 



The horizontal distribution of the plankton is consequently 

 liable to be very variable and irregular, and although its character- 

 istic constitution at different times of the year may be described, 

 and the relative abundance of the different groups discussed, it 

 is very doubtful whether any numerical estimates can be framed 

 which will be applicable to wide areas. 



It is clear that samples taken quarterly, monthly, or even fort- 

 nightly, are quite inadequate to convey a correct idea of the 

 constitution and changes of the plankton of a sea-area in any 

 detail ; and, consequently, conclusions ought not to be drawn from 

 such insufficient observations. Samples, taken weekly throughout 

 the year, and almost daily during the three most critical months, 

 give by no means too much information, but will probably suffice 

 to enable one to make that detailed comparison between adjacent 

 localities and dates which are necessary for the purpose of 

 determining the representative value of such periodic samples. 



In thinking of this address last winter there was another 

 subject that I hoped to have laid before you. It was a com- 

 parison of the conditions of a certain fishing bank in the Irish 

 Sea 70 years ago and at the present time, and it seemed to me 

 that this would be a particularly appropriate study to lay before 

 this Society since it involved questions of Zoology, Botany, and 

 Greology combined which might interest many of our Fellows. 

 I started some of the necessary investigations at sea last summer 

 and hoped to have completed them this Easter, but unfortunately 

 winds and weather were such in the Irish Sea during April that 

 I could not get near to the bank in question. Consequently, the 

 research is still incomplete, but it may interest you to have the 

 problem briefly stated, and I shall hope on some future occasion 

 to publish the results obtained. 



In the 'Annals and Magazine' for 1839 Professor Edward 

 Forbes published a short paper entitled, " On a Shell-bank in the 

 Irish Sea, considei'ed Zoologically and Greologically " (Ann. & 

 Mag. Nat. Hist. vol. iv. 1840, p. 217), in which he recorded the 

 results obtained during some years of occasional dredging on a 

 scallop bank lying opposite Ballaugh off the North- West of the 

 Isle of Man. As these observations extended over seven years 

 previous to 1839, if we reckon from a period about the middle of 

 his Mork we may consider that we are now dealing with a record 

 of the condition of the marine fauna on this bank well over 

 70 years ago. It seemed to me that we had here an opportunity, 

 such as rarely occurs, of determining whether any change had 

 taken place in a limited, well-defined area after a considerable 

 interval of time. Forbes, unfortunately, did not deal with all 



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