->J0 



MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



body. Reflected tabulation deduced from linear complexes of 4', 6", 5'", ip, 1"". 

 Processes slender, solid, taeniate, united half to two-thirds along their length by 

 membranes or trabeculae. Processes distally unconnected and unequally bifurcate. 



Holotype. B.M.(N.H.) slide ¥.51977(2). London Clay ; Enborne, Borehole 

 E ii, 61 ft. 



Dimensions. Holotype : diameter of central body 61 by 73^. Length of proces- 

 ses up to 36^. Observed range : diameter of central body <\i-j^\l, length of processes 

 up to 40[x. Number of specimens measured, 4. 



Description. This species is unusual in that it possesses processes restricted to 

 the ambitus yet which are grouped into linear or sometimes arcuate complexes 

 reflecting a dinoflagellate tabulation. The apical archaeopyle is nearly always 

 developed and had a clear sulcal notch. The precingulars possess a variable number 

 of processes, plates 1", 2", 4" and 5" having well-developed linear complexes, 3" 

 having a complex of varying extent, whilst 6" can be devoid of processes. 



The processes are not unlike those of Areoligera medusettiformis (O. Wetzel). The 

 interconnecting membrane sometimes extends to the base of the processes and, if so 

 developed, is often fenestrate proximally. Distally the processes are bifurcate 

 commonly with one fork longer than the other and recurved. Occasionally the 

 processes are acuminate. Branching can occur distally to the interconnecting 

 membrane or trabeculae. 



Occurrence. Eocene, London Clay ; Whitecliff and Enborne. 



B 



ARCHAEOPYLE 



Fig. 62. Cyclonephelium ordinatum sp. nov. Holotype. a, Tabulation of the upper 

 (dorsal) surface, b. Tabulation of the lower (ventral) surface seen through the upper, 

 c, Partial drawing to show the ziz-zag nature of the archaeopyle margin. 



