The Microplankton of Plymouth Sound from the Region 
beyond the Breakwater. 
By 
Marie V. Lebour, M.Sc., 
Assistant Lecturer in Zoology, Leeds University. 
Temporary Naturalist at the Plymouth Laboratory. 
With Figures 1-9 in the text, and Tables I and II at the end. 
THROUGHOUT a complete year from September, 1915, to September, 
1916, sea-water samples were taken regularly two or three times a week 
from beyond the Breakwater in the region of the Knap buoy, 23 miles 
from Plymouth shore, from the surface and at 5 and 7 fathoms. The 
object was to supplement the existing records from the tow nets as it 
is well known that a very large amount of material is lost even from the 
finest nets, as Lohmann has shown exhaustively (1908). So far the 
only plankton records from this region have been from the tow nets, 
and a glance at the tables given at the end of this paper will show directly, 
if compared with those by Gough (1903-7) and Bygrave (1911), also 
Cleve (1899 and 1900), the great difference in numbers of the smaller 
forms, or their entire absence from the tow nettings. Again, no actual 
numerical records have been given from this region. At the same time 
as the water samples were taken, tow nettings, coarse, medium and 
very fine, were also secured, and these were regularly examined for 
comparison. 
The water samples were estimated by means of the centrifuge after 
the manner introduced by Lohmann. A water-bottle was used for the 
5 and 7 fathom samples, and the surface sample was collected in a Win- 
chester bottle. Experiment showed that there was no difference in 
the surface samples when collected either with the water-bottle or Win- 
chester, and it was found more convenient for keeping as it was unnecessary 
always to examine it the day of collection, as was the case with the water- 
bottle samples. The Winchester samples keep for two or three days at 
a uniform temperature. If examined the day they are brought in the 
water-bottle samples are quite as good as the surface samples in the 
NEW SERIES—VOL. XI. NO. 2, MAY, 1917. K 
