MESOZOIC AND CAINOZOIC DINOFL AGELL ATE CYSTS 231 



Dimensions. Diameter of central body 70 by 85jjl. Length of processes up to 



28(X. 



Occurrence. Eocene, London Clay ; Sheppey, Kent. 



Remarks. A. cf. senonensis, like A. cf. medusettiformis and A cf. coronata is a 

 form approaching the genus Systematophora. The London Clay forms attributed to 

 Areoligera, differ from Systematophora only because of the presence of process com- 

 plexes on the central surface, in particular on plate 6" which is usually barren of 

 processes. 



Genus DEFLANDREA Eisenack 1938 : 187 



Emended diagnosis. Cavate cysts with periphragm forming elongate pentagonal 

 (also often somewhat rounded to rhomboidal) outer shell. Lateral walls usually 

 convex. One apical and two antapical horns, more or less reduced. Tabulation, 

 when decipherable, peridinoid. Periphragm smooth or granular. Cingulum circular 

 longitudinal furrow if observable restricted to hypotract. Inner capsule circular to 

 ovoidal in outline ; endophragm of variable thickness. Archaeopyle intercalary. 



Type species. D. phosphoritica Eisenack 1938. Oligocene ; East Prussia. 



Discussion. The genus Deflandrea is represented by a large number of species, 

 some of which clearly overlap. To avoid further confusion, many specimens figured 

 are not given a specific name or detailed description since slight changes in outline of 

 the pericoel are not considered worthy of specific differentation. 



Deflandrea phosphoritica subsp. phosphoritica Cookson & Eisenack 



PI. 26, figs. 2, 3, 6, 9 



19616. Deflandrea phosphoritica subsp. phosphoritica Cookson & Eisenack : 39. 



Discussion. This subspecies, common in the London Clay, often possesses a 

 clearly marked indented circular cingulum and a sulcus restricted to the hypotract 

 and widening posteriorly. The outline of the periphragm varies from being identical 

 to the type material to closely approaching Deflandrea phosphoritica subsp. australis 

 Cookson & Eisenack 1961, which has a more granular periphragm and a short solid 

 cylindrical process at the distal extremity of the apical horn and frequently more 

 pronounced antapical horns. 



A few specimens without a capsule were observed ; in one the interior was empty, 

 in the others formless organic matter appeared to have formed from decay of the 

 capsule. 



The archaeopyle of the London Clay specimens of D. phosphoritica subsp. phos- 

 phoritica is always intercalary in the periphragm but appears to occupy a more apical 

 position in the endophragm. The granules on the surface of the periphragm often 

 delimit plate boundaries and also tend to show linear alignment, running from the 

 apex towards the antapex. 



