8 MR. B. M. GRIFFITHS ON THE 
of aquatics may harbour different communities of alge, the various plant- 
associations met with in small pools will again tend to accentuate the 
differences in the planktons. 
SPECIES OF SPECIAL INTEREST. 
1, Perıpinivm Wirte Huitf.-Kaas., West, Algæ 1916, p. 62. 
This Peridinian occurred plentifully in the two Bulmershe pools. In the 
South Pool it occurred alone, but in the North Pool it was associated with 
P. cinctum. It is widely distributed in the larger lakes of the British Isles 
(West & West, 1909), but it has not been found in any of the Worcestershire 
or Warwickshire pools. Its occurrence in a relatively small pool is there- 
fore of some interest. P. Wille resembles P. cinctum, differing mainly in 
the shape of the third apical interealary plate and in the slight median 
asymmetry of the plates of the hypovalve. It also closely resembles 
P. Volzü, Lemm., var. australe, G. S. West (West, 1901 i), the chief 
difference being in the even more marked asymmetry of the hypovalve of 
the latter. The diagram of the plates of P. Willei, given in the * Süsswasser- 
flora," Heft 3, p. 45, fig. 51, differs considerably from that given by West. 
The identifieation has been made from West's figures, as they seem less 
diagrammatie than the others. 
2. PERIDINIUM SuTTONT, sp. nov. (Pl. 1. figs. 1-6.) 
This species formed one of the dominant constituents of the plankton of 
Whiteknights Pool. It appears to differ from any species previously 
described. The epivalve is more or less conical and slightly longer than the 
hypovalve. The latter is hemispherical and provided with short, stout 
spines, Using the nomenclature of Kofoid (see West, Alge, 1916, p. 15), the 
structure of the cell-wall is as follows :— 
The plates of the epivalve comprise 6 precingulars, 4 apicals bounding the 
somewhat elongated pore, and 1 pentagonal apical intercalary plate sur- 
rounded by 2", 5", 4" and 2', 3' (Pl. 1. figs. 3,5). The hypovalve is medianly 
symmetrical, consisting of 5 postcingulars and 2 equal antapicals (figs. 4, 6). 
Each of the postcingular plates except No. 3, and both the antapical plates, 
bear one broad-based conical spine more or less centrally placed. Occa- 
sionally there are two spines on each antapical plate and none on the Nos. 2 
and 4 postcingulars (fig. 6). 
All the plates are minutely punctate. Intercalary bands may develop 
between the plates, but as a rule those between the apical plates remain 
narrow. There is an elongated and sinuous flagellar pore in the ventral 
groove. 
Most of the specimens were either empty or their contents were aggre- 
gated into cysts. The alga is therefore most probably an early summer 
