The Peridiniece of Sutton Park, Warwickshire. 191 
anterior half of the cell-wall. These cannot all be seen at the same 
time in a truly anterior view (Fig. 24 D), but in a slightly oblique 
view they are all visible (Fig. 24 E). 
P. cinctum var. Lemmermanni attains an enormous maximum in 
August or September, and as no thin-walled cysts are formed com¬ 
parable to those observed in P. a«g7icM/;qthisgreatnumerical increase 
must be due to some other cause. Two possible explanations suggest 
themselves. The great maximum could be produced by rapid 
Fig. 24. Peridinium cinctum Ehrenb. var. Lemmermanni var. n. A and B, 
ventral views ; C, dorsal view; D, epivalve ; E, epivalve seen somewhat 
obliquely ; F, hypovalve. The numerals I.—VII. and I.—V. refer to the 
equatorial plates of the epivalve and hypovalve respectively ; r, rhomboidal 
plate; va, and va 2 , ventral apical plates; da, — da 4 , dorsal apical plates; ant , 
and ant 2 , antapical plates. All x 500. 
division while in the motile Peridinium- stage, but this seems 
scarcely probable in view of the fact that in this species I have 
never at any time observed a case of division of the adult motile 
cell. The most likely explanation is that of a gradually increasing 
rate of development from the resting-cysts in the period from May 
to August, culminating in a maximum rate of development in the 
latter month, accompanied by cell-division in the Gymnodinium- 
stage through which all developing Peridinia have to pass. 
It seems highly probable that many of the records of P. 
tabulatum really refer to P. cinctum, as Bergh, 1 Klebs 3 , and Penard 3 
1 Bergh in Morpholog. Jahrbiich, 1881. 
2 Klebs in Arb. botan. lnstit. Tubingen, 1883, t. 2, f. 22—24, 28. 
3 Penard in Bull. Soc. Botan. Geneve, 1891, t. 2, f. 8—16; t. 3, 
f. 1-2. 
