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HELEOPLANKTON OF THREE BERKSHIRE POOLS. 9 
form, and the collection was taken at the end of its phase. The associated 
P. anglieum was in the same condition. 
The species has been namel after the family of Sutton, whose name is 
closely associated with the Reading district, and whose contributions to horti- 
cultural and agricultural botany are well known. 
DiaGnosis, Peridinium Sultoni, sp. nov. ; corpore in partibus inæqualibus 
duabus a fossa transversa diviso, parte apicali vel anteriori conicali, parte 
inferiori vel posteriori semisphæricali ; fossa transversa æquatoriale disposita. 
Epivalva e tabulis 11 composita ; tabulis preeingularibus 6, tabulis api- 
calibus 3, tabula intercalaria 1. 
Hypovalva e tabulis 7 composita ; tabulis antapicalibus æqualibus 2, uni 
vel duobus spinis conicalibus ornatis ; tabulis posteingularibus 5, e quibus 4 
plus vel minus medialibus spinis conicalibus ornatze sunt. Tabula punetu- 
latæ delicatissimæ. 
3. PERIDINIUM BIPES, Stein, and var, EXCISUM, Lenm. 
The type-form and the variety occurred together in both the Bulmershe 
Pools. The type-form was much less numerous than the variety. The 
specimens also were more tumid and less attenuate than is shown in the 
figure given in the Siisswasserfl., H. 3, p. 36. Occasionally forms were 
found in which the basal spines were dentate (see Pl. 1. fig. 7). 
4. IRHIZOSOLENIA LONGISETA, Zach. 
The diatom was found in very small numbers in Whiteknights Pool. It 
occurs in the plankton of some of the Scottish lakes and in pools on the 
Continent, but it is an uncommon alga. Three specimens are figured (Pl. 1. 
fig. 9) to show variations in size. 
5. BrEPHANODISCUS HaNTZsCHIANUS, Grun. (British F. W. Alge, G. S. 
West, 1904, fig. 127 A, p. 277). ` , 
This diatom also occurred in Whiteknights Pool in very small numbers 
associated with Cyclotella Kuetzingiana and Synedra Acus. It has been 
recorded in the British Isles from Lough Neagh, and is a distinctly rare alga. 
6. LAGERHEIMIA WRATISLAVIENSIS, Schroeder. (Pl. 1. fig. 8.) 
The alga occurred in very small numbers in Whiteknights Pool. It is 
distinguished from similar species by the position of the spines, which are 
placed in alignment with the major and minor axes of the cell. Tt is recorded 
twice for the English Midlands (Grove, 1920, p. 27), and it is a sporadic 
constituent of Continental pools, but is not commonly found. 
7. CRUCIGENIA TgrRAPEDIA (Kirchn.), W. & G. S. West. (P1.1. fig. 11.) 
This organism was found in very small numbers in Whiteknights Pool. 
Only colonies of four cells were seen. It is recorded from the plankton of 
Lough Neagh and from that of the Oder. 
