I94 8 - 

 1955- 



MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Cyclonephelium exuberans Deflandre & Cookson 

 Text-fig. 61 



Membranilarnax pterospermoid.es Pastiels : 46, pi. 5, figs. 11-14. 

 Cyclonephelium exuberans Deflandre & Cookson : 281. 



225 



Discussion. C. exuberans has probably evolved from C. pastielsi, intermediate 

 forms between the two being common. Specimens from the London Clay show the 

 same variation in process distribution as C. pastielsi, some individuals lacking 

 processes on plates 3" and 6", others having processes on all the precingular plates, 

 although generally with fewer on 3" and 6" than on the others. The prominent 

 sulcal notch lies to the right of the mid-ventral line. The surface of the central body 

 is commonly granular. 



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

 56-85^, length of processes up to 46^. Number of specimens measured, 4. 



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

 (Ypresian) of Belgium (Pastiels 1948). 



Cyclonephelium ordinatum sp. nov. 

 PI. 25, fig. 3 ; Text-fig. 62 



Derivation of name. Latin ; ordinatus, in row, orderly. 



Diagnosis. Thin walled central body with granular surface. Processes formed 

 from periphragm and restricted to linear complexes regularly distributed on central 



PRECINGULAR 

 PROCESS 



Fig. 61. Cyclonephelium exuberans (Pastiels). Partial drawing showing large precingular 

 processes around the margin of the archaeopyle (broken line). 



