MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 37 



stability being reached in the Eocene when the processes resemble those found in 

 H. ramosa var. ramosa but are shorter and subconical, and considerably more 

 numerous. H. ramosa var. multibrevis is similar to H . furcata var. multiplicata 

 (Rossignol 1964) from the Pleistocene of the Eastern Mediterranean except for the 

 absence of the two distinctive large dorsal antapical processes. 



H. ramosa var. multibrevis has been recorded from the Lower Cretaceous (Hauteri- 

 vian) to the Eocene (Ypresian) in England, from the Upper Cretaceous of France and 

 from the Aptian of Germany. 



Hystrichosphaera ramosa var. membranacea (Rossignol) 

 PI. 4, figs. 8, 12 



1964. Hystrichosphaera furcata var. membranacea Rossignol : 86, pi. 1, figs. 4, 9, 10 ; pi. 3, 

 figs. 7, 12. 



Material (Figured). B.M.(N.H.) slide ¥.51747(2). Metropolitan Water Board 

 Borehole No. 11 at 53 feet depth, London Clay ; Enborne, Berkshire. Micropal. 

 Lab., Sheffield University No. SL5. 173 ft. above base of London Clay ; Sheppey, 

 Kent. 



Dimensions. ¥.51747(2) : diameter of central body 38- 5 by 43^, length of processes 

 up to 19^. Observed range : diameter of central body 3i , 5-45f x < length of processes 

 up to 26jjl. Number of specimens measured, 5. 



Remarks. The specimens belonging to this variety found in the London Clay 

 agree fairly well with those observed by Rossignol (1964) from the Pleistocene. 

 H. ramosa var. membranacea possesses a smooth walled central body with well 

 developed membranes on the plate boundaries. The membranes are variable in 

 height and development and may unite all or only few of the processes. However 

 the membranes are commonly well developed only in the cingular and polar regions. 

 The two large dorsal antapical processes noted by Rossignol are not noticeable in the 

 Eocene forms. 



The often extensive development of a membrane in the equatorial zone restricted 

 to one side gives some of the specimens a superficial resemblance to the form figured 

 as H. ramosa by Lejeune (1937). 



Hystrichosphaera ramosa var. granomembranacea nov. 



PI. 4. ng. 4 



Derivation of name. Latin, granosus, granular ; membrana, membrane— 

 with reference to the granular membranes present in this variety. 



Diagnosis. A variety of H. ramosa (Ehrenberg) possessing a central body with a 

 granular surface. Membranes well developed on plate boundaries particularly in 

 cingular and polar regions. 



