160 HULL SCIENTIFIC AND FIELD NATURALISTS’ CLUB. 
As regards the extent of country to be considered as the 
‘- Hull District,” we have followed Norman in not confining 
ourselves too closely to the immediate neighbourhood of the 
City. His records comprise gatherings from places, in a few 
cases, as far distant as Harrogate and Whitby. Speaking 
generally, we have assumed any place to be in the district 
that is within reach of a half-day excursion from Hull. The 
only species we have omitted from his list are those he records 
on ships’ bottoms from foreign parts, as these cannot fairly 
be considered local. Early in our work, the question arose 
as to whether we should be justified in including species 
which Norman found only in the stomachs of Ascidian 
Molluscs, adhering to oyster shells bought in the Hull market, 
but the evidence being conclusive that these were dredged up 
from the North Sea, and the fact that we have found many 
of these Ascidian species on the shores of the Yorkshire coast 
and in the Humber estuary, renders it pretty certain that 
the whole of them may be found, after more numerous 
observations, within our limits. | Norman regretted not 
having been able to make many gatherings from the sands 
of the sea shore, and unfortunately we have to express 
the same regret. The conditions under which gatherings 
may be made from marine sands are so fugitive that 
opportunities of making them are exceedingly scarce. 
Our material from the North Sea is somewhat scanty. It 
consists merely of a few Ascidian gatherings examined by 
Norman, some plankton diatems on the authority of Prof. T. 
P. Cleve, and a deepsea sounding. There is therefore a wide 
field for the labours of our members who are fond of the sea. 
. A careful perusal of Prof. Cleve’s works on the plankton of 
the North Sea and neighbouring waters will afford much 
valuable information as to the seasonal distribution of the 
numerous diatoms inhabiting them. We have, however, only 
thought it desirable to record the forms found by him in a 
gathering taken near the Yorkshire coast at long. 0° 5’ W., 
lat. 55° 20’. The diatoms from this gathering are identified 
in the following list thus :—(Cl.). 
The plankton diatoms are of great interest and teach us 
much about oceanic currents. The neritic (litoral) forms are 
in many cases varieties of the oceanic, and pass suddenly from 
one to the other—e.g., Rhisosolenia alata becomes changed 
into R. gracillima, and it is not an uncommon occurrence to 
find a specimen one half of which is typical of R. alata and 
the other half of R. gracillima. Again, the northern varieties 
on inhabiting more temperate waters change their appearance, 
