72 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Dimensions. Neotype : diameter of central body 35 by 35^., length of processes 

 22-25^. Range : diameter of central body 34-55^, length of processes 22-4310.. 

 Number of specimens measured, 9. 



Description. In the specimens from the Cenomanian, the periphragm of the 

 central body is smooth or very slightly granular. The processes are cylindrical for 

 most of their length, with an expanded opening distally, the margin of which is 

 developed into aculei and secae. The aculei and secae can be simple or branched, 

 erect or patulate, orthogonal or even recurved. Where the processes meet the central 

 body there is often a clearly marked ring indicating the point of divergence of the 

 endophragm and periphragm. The wall of the processes is smooth or faintly 

 fibrous ; their length usually measures between the radius and the diameter of the 

 central body. 



The small number of processes and the apical archaeopyle, when present, enable 

 one readily to determine the tabulation of 0. complex as reflected by the position of 

 the processes. 



Specimens of 0. complex have been examined from two other horizons. 



Examples from the Speeton Clay (Barremian) of Yorkshire are very similar to 

 the forms illustrated by Eisenack (1958). The periphragm of the central body is 

 often slightly granular and some of the processes are more deeply divided and show 

 more variation than is usual in this species. 11 specimens were measured, the 

 diameter of the central body being 35-62(1 and the length of the processes 13-471X. 



Specimens from the London Clay (Ypresian) strongly resemble the Cenomanian 

 forms, the processes perhaps being a little stouter. Diameter of central body 

 2g-$8\i, length of processes 23-39^ (6 specimens measured) . 



Fig. 14. Oligosphaeridium complex (White). A specimen from the Cenomanian, in lateral 

 view, showing the angular apical archaeopyle and the distribution of the processes. 

 X c. 420. 



