i 9 8 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



girdle is also less well marked whilst the capsule archaeopyle gives the impression of 

 being apical in some specimens. This may be due to secondary movement of the 

 capsule within the pericoel. The capsule is occasionally found free. 



On the outer surface of the periphragm of some individuals are present dendritic 

 ridges, radiating out from central points and being up to 10 or 15^ across. They are 

 not caused by local thickenings of the wall but by undulations. On an individual 

 there can be a large number of these dendritic radiating structures. They are 

 possibly a result of fungal attack. W. glabra is included in the sub-genus Rhombo- 

 dinium on account of the absence of processes. 



Dimensions. Range observed in London Clay : outer shell, length i^o-i^i\i, 

 breadth 147-168^. Capsule, length 66-8o[i, breadth 69-76^. Number of speci- 

 mens measured, 6. 



Occurrence. Eocene, London Clay ; Sheppey, Kent. Eocene ; Australia 

 (Cookson 1956). 



