G. S. West. 
190 
plates of the hypovalve (consult Fig. 23 A and D) constitute one of 
the characteristic features of P. anglicum. All the plates are 
irregularly dotted with very minute spine-like projections. 
Diagnosis: —Peridinium anglicum, sp. n. P. circiter lj-plo 
longius quam latum ; corpore in partibus subaequalibus duabus a 
fossa transversa diviso, parte apicali (vel anteriori) rotundo-conica, 
parte inferiori (vel posteriori) depresso-rotunda ; fossa transversa 
subspiraliter disposita; fossa longitudinali a parte apicali pane 
exclusa. Epivalva e tabulis 11 composita, tabula rhomboidea juxta 
apicem extensa ; tabulis apicalibus dorsalibus rhomboideo-rectangu- 
laribus 2, tabula apicali ventrali rectangulari singula; tabulis 
aquatoriis 7. Hypovalva e tabulis 7 composita ; tabulis antapi- 
calibus (posterioribus) aqualibus 2, marginibus spinis conspicuis 
paucis ornatis; tabulis aquatoriis 5. Tabula tota spinulis 
minutissimis irregulariter ordinatis et subsparsis ornata. Cysta 
globosa vel subglobosa, membrana glabra. Long. 50-58/x; lat. 
42-48//.; crass, max. 33/x; diam. cyst. 35-41/u 
V. —Peridinium cinctum Ehrenb. var. Lemmermanni. 
This is the largest of the Peridinia found in Bracebridge 
Pool, and is easily recognized by its outward form and the 
disposition and areolation of the plates composing the cell-wall. 
It is a decided summer or warm-water species, making its first 
appearance in the plankton in April or May, and attaining its 
maximum in August or September, with a water-temperature of 
17—19 n C. From this time there is a rapid decline in numbers, 
until by the end of October or November the organism has 
completely vanished. 
The formation of thick-walled resting-cysts was observed in 
October (Fig. 20 J). These were very large, and by the time they 
were fully formed the old wall of the mother-cell was generally 
dislocated and partially thrown off. 
The specimens agree in the general disposition of the plates 
with the descriptions and figures of P. cinctum Ehrenb., but the six 
apical plates of the epivalve (m p va 2 , da } , da 2 , da 5 and da 4 ) are 
considerably larger and in consequence occupy a much greater 
superficial area. The most dorsal of the equatorial plates of the 
epivalve (No. IV. in Fig. 24 E) is also much larger than in typical 
P. cinctum. 
There are altogether fourteen plates composing the epivalve or 
