HELEOPLANKTON OF THREE BERKSHIRE POOLS. 5 
THE ALGA-FLORA. 
The marked individuality of planktons noticed in the pools of North 
Worcestershire (Griffiths, 1916) was found to hold in the case of the 
Berkshire pools. The planktons are so different that a single glance under 
the microscope is sufficient to distinguish them from each other, 
The dominant plankton constituents, arranged in order of abundance, are 
as follows :— 
» a 0 D . à 
I. Bulmershe North Pool. Ceratium Hirundinella (three-horned form), 
Tribonema affine, Dinobryon Sertularia, Peridinium Willer, P. cinctum, 
P. bipes, Dictyospherium pulchellum. 
2. Bulmershe South Pool. Ceratium Hirundinella (two-horned form), 
Closterium aciculare var. subpronum, Peridinium Willei, Eudorina 
elegans, Cosmarium Meneghinii, Peridinium bipes, Volvox aureus. 
3. Whiteknights Pool. Ceratium Hirundinella (three-horned form), Syn- 
edra Acus, Peridinium Suttoni, Pandorina morum, | Peridinium 
anglicum, Tribonema affine, Cyclotella Kuetzingiana. 
It will be seen from the above table that the most abundant organisms 
of the plankton are the Peridinieæ, no less than eight species being present 
in the three pools. In this respect the pools differ from those of North 
Worcestershire, but resemble that of Bracebridge Pool, Warwickshire 
(West, 1909 ii). One species, P. Suttoni, occurring abundantly in White- 
knights Pool, is new, and P. Willei, found in quantity in the two Bulmershe 
pools, has not been recorded previously for small lowland pools. P. Willei 
closely resembles P. cinctum, with which it was associated in Bulmershe 
North Pool. P. anglicum was originally described from Bracebridge Pool, 
and it also occurred in Stanklin Pool, Worcs. (Griffiths, 1912, 1916). It 
formed a considerable proportion of the plankton of Whiteknights Pool, in 
association with P. Suttoni. 
In every pool the bulk of the plankton consisted of Ceratium Hirundinella. 
The form with three basal horns occurred in both Bulmershe North and 
Whiteknights, but the twc-horned form was confined exclusively to 
Bulmershe South. The two three. horned forms were not absolutely identical. 
It is notable that the two Bulmershe pools, in spite of their close proximity, 
contained entirely distinct forms of the organism, whereas the more distant 
Whiteknights had a form practically identical with that of Bulmershe North. 
Peridinium bipes occurred in both Bulmershe pools, and in each instance 
included the type-form together with the variety exeisum. 
Peridinium inconspicuum has been found previously in Bracebridge Pool. 
* 
It was fairly frequent in Bulmershe South. 
