BY G. I. PLAYFAIR. 815 



of its ridged membrane this form should be placed under P. 

 Westii Lemm. The latter, however, belongs to the P. cinctum 

 group, while the diagram of the epivalve shows that P. australe 

 must be grouped with P. Willei Huitf eld-Kaas . 



The membrane is covered all over with coarse irregular dis- 

 jointed ridges running longitudinally. All the plates in dorsal 

 view are very broad. The epivalve is greatly compressd towards 

 the apex so as to form there a transverse apical ridge composed 

 of 3 very narrow plates which cannot be said to be either dorsal 

 or ventral. The central one of these is small and exactly rect- 

 angular, sometimes so indistinctly delimited that all three ap- 

 pear to f crm a single plate . In the hypovalve the two antapical 

 plates have coalesced to form a single plate with rounded out- 

 line, a slight notch on the dorsal side and an indistinct suture 

 alone showing that the two are of unequal size. 



Peridinium zonatum mini. (PL xliii., f. 3) . 



Peridinium magnum, globosum; fossa transversa, spirali, sub- 

 mediana, di visum; membrana glabra; tabulis omnibus (antapic- 

 alibus exceptis) rugis incrassatis, rectis, parallelis, binis, trans- 

 verse dispositis ornatis; tabulis antapicalibus ut in P. australi 

 rugulosis. Epivalva heniisphaQrica rotundata baud angulata; 

 tabulis aequatoriis 7; tabulis subapicalibus dorsalibus 2, ven- 

 tralibus 2; tabula apicali una, laterali una. Hypovalva hemis- 

 phaerica, rotundata, baud angulata; tabulis aequatoriis 5, apicali- 

 bus 2 in tabulam unam subcirculatam coalitis. 



Long. = lat. = 50-54 p. Sydney Water Supply (100, 102, 

 115). 



Syn. Peridinium tabulatum var. zonatum Playf., I.e., p. 543, 

 PL lv., f . 10-12. This species seems to belong to the P. cinctum 

 group along with P. granulosum and P. Westii. In dorsal view 

 the markings are those of P. caudatum var. guild fordense when 

 the cell is in a certain position, but on turning the cell a little, 

 the edge of another (the lateral) plate comes immediately into 

 view. The arrangement of plates in end view of the epivalve 

 is difficult to make out exactly but seems to be on the lines of 

 P. cinctum. There are 2 subapical ventral plates, 2 distinctly 

 dorsal, one almost exactly apical and one lateral. In the hypo- 

 valve there are two antapical plates usually coalesced into one 

 with a subcircular outline. Karely two regular distinct antapical 

 plates are formed (PL xlii., f. 9). The ridging here is that of 



