THE OSTRACODA. 



307 



Vertical Open Nets, such as have 1)een in fashion on recent expeditions. For the 

 serious study of plankton such hauls are a mere waste of time and energy, however 

 much they may fill museums and multiply species. 



Prom this haul, by itself, nothing could be deduced except that the species included 

 were all present somewhere between 1250 fathoms and the surface, on a particular date, 

 at a particular geographical position. Coutemporary observations showed further that 

 the range of possible temperatures was about 3"^ to 17°'5 C, temperatures which 

 correspond roughly to the mean surface temperatui-es of Grihraltar and Archangelsk ! 



These verticc^l hauls do not even give a means of estimating the proportions in which 

 the various species are present in the area. This is shown by a comparison of the per- 

 centage which each species constituted of haul 27 a (second column of the table below) 

 with tlie percentage which these same species formed of the total (actual) numbers 

 captured during the cruise (third column). The fourth column gives the real distribution 

 of the species at the date and time of the cruise as deduced above from a comparison of 

 all the comparable hauls made; it shows — if, indeed, it be necessary to show it — what 

 a mixture of different faxmas is brought to the surface by such a method of capture. 



Missing altogether were, not only the scarce forms brachyaskos, pusilla, and spinirostris, 

 but also the fairly common forms imbricala, spinifera, and globosa. 



Except as regards the common species citrta, rotundata, and magna, the percentages 



SECOND SERIES. — ZOOLOGY, VOL. X. 49 



