MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 223 



Cannosphaeropsis reticulensis Pastiels 

 PL 24, fig. 8 



1948. Cannosphaeropsis reticulensis Pastiels : 49, pi. 5, figs. 7-10. 

 1961. Cannosphaeropsis reticulensis Pastiels ; Alberti : 36, pi. 9, fig. 15. 



Discussion. Specimens of C. reticulensis possessing a precingular archaeopyle 

 with gonal and sutural processes, are present in the London Clay. The intercon- 

 necting trabeculae appear to be solid, taeniate and not tubular. The simple acumi- 

 nate spines arising from the trabeculae of the type material are uncommon in the 

 London Clay forms. 



Dimensions. Range observed in London Clay : diameter of central body 

 26-43^, length of processes 9-i8[a. Number of specimens measured, 5. 



Occurrence. Eocene, London Clay ; Whitecliff, Enborne and Sheppey. 

 C. reticulensis is also known from the Eocene of Belgium (Pastiels 1948) and Germany 

 (Alberti 1961). 



Genus CYCLONEPHELIUM Deflandre & Cookson 1955 : 285 



Emended diagnosis. Chorate cysts with central body flattened dorso-ventrally 

 and apparently concavo-convex, outline circular to slightly oval. Apex and/or 

 antapex with or without blunt prominence, antapex occasionally slightly indented. 

 Ornamentation restricted to circumferential zone of varying width, consisting of (1) 

 processes, of varying lengths and shapes, distinct or more or less confluent, (2) thin 

 membrane supported at intervals by strong processes, or (3) densely arranged surface 

 thickenings. Ornamentation sometimes more strongly developed in antapical 

 region. Archaeopyle apical tetrabular. Wall layers not distinguished. 



Type species. Cyclonephelium compactum Deflandre & Cookson 1955. Lower to 

 Upper Cretaceous ; Australia. 



Discussion. Tabulation cannot be determined in this genus beyond the fact that 

 there are four apical and six precingular plates. This is apparent from an examina- 

 tion of a detached operculum and the margin of the archaeopyle, which is zigzag. 



The shape of specimens of Cyclonephelium is variable and is probably partly 

 dependent on subsequent compression in the enclosing sediment. Individuals of the 

 species C. exuberans Deflandre & Cookson 1955, are often similar to Areoligera in 

 having a convex dorsal surface and a depressed ventral surface. This is not, 

 however, universal, since others appear to have an ellipsoidal outline, both dorsal and 

 ventral surfaces being convex. 



Cyclonephelium divaricatum sp. nov. 



PL 25, fig. 1 ; Text-fig. 60 



Derivation of name. Latin ; divaricatus, spread apart. 



Diagnosis. Central body flat or slightly convex with circular outline bearing 

 numerous ambital taeniate processes. Processes united distally in complex 



