MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 167 



Cleistosphaeridium diversispinosum sp. nov. 

 PL 10, fig. 7 



Derivation of name. Latin, diversus, different ; spinosus, thorny — with 

 reference to the variable shape of the processes. 



Diagnosis. A Cleistospharidium with granular wall and polygonal archaeopyle. 

 Processes solid, taeniate or tubular, usually slender and proximally expanded. 

 Distal end forked or expanded. 



Holotype. B.M.(N.H.) slide ¥.51750(1). Eocene (London Clay) ; Whitecliff. 



Dimensions. Holotype : diameter of body 38^, length of processes, g-i6\i. 

 Observed range : diameter of body 38-43^, length of processes 7~23[x. Number of 

 specimens measured, 5. 



Description. This species is distinguished by the variable nature of the process 

 ends. The expanded termination may be bifurcate, orthogonal or patulate, one 

 branch may be larger than the other. The edges are usually denticulate and the 

 processes may be up to 5;x wide ; but are usually about 2jx. There is more than one 

 process to a plate. 



Occurrence. London Clay ; Whitecliff, Enborne and Sheppey. 



Remarks. Only Cleistosphaeridium pectiniforme (Gerlach) 1961 comb. nov. 

 resembles C. diversispinosum to any degree. It has widely forked processes with 

 spinose margins ; it does not, however, have the variability of process ending shown 

 by our species. The species pectiniforme is reattributed to the genus Cleistosphaeri- 

 dium provisionally on the basis of its similarity to C. diversispinosum, despite lack 

 of knowledge of its mode of archaeopyle formation. 



Cleistosphaeridium ancoriferum (Cookson & Eisenack) 



PI. 9- %• 1 



1960a. Hystrichosphaeridium ancoriferum Cookson & Eisenack : 8, pi. 2, fig. 11. 

 1964. Hystrichosphaeridium ancoriferum Cookson & Eisenack ; Cookson & Hughes : 47, pi. 9, 

 fig- 7- 



Description. The specimens of C. ancoriferum found in the Lower Cenomanian 

 of England, first described and figured by Cookson & Hughes (1964) strongly resemble 

 those examples recorded from Australia (Cookson & Eisenack, 1960a). Many of the 

 specimens from the Fetcham Mill Borehole possess a 6-sided apical archaeopyle 

 the shape of which is often difficult to determine due to distortion. However, 

 detached apical regions are relatively abundant. The processes are hollow, the 

 cavity often being constricted to some extent, and closed distally and proximally. 

 They do not appear to be aligned to any noticeable extent. 



C. ancoriferum has been recorded from the Albian and Cenomanian of England and 

 Australia. 



