MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



143 



Holotype. Preparation No. A26, Geologisches Institut der Universitat, Tubing- 

 en, Germany. Lower Cretaceous (Upper Barremian) ; Haverlahwiese, Germany. 



Material (figured). Geol. Surv. Colin, slide PF.3035(4). Chalk, H. M. Geological 

 Survey Borehole, Fetcham Mill, Surrey, at 840 feet depth. Upper Cretaceous 

 (basal Cenomanian). 



Dimensions. Holotype : shell length 48^1, breadth 38jx, length of processes 

 i6-22[jl. Range of German specimens : shell length 48-60^, breadth 38-56^, 

 length of processes i6-36fi.. Specimen here figured : overall length c.12$\l, breadth 

 c.io5[x : shell length 62fi,, breadth 45jx. 



Description. This species occurs in low numbers in the assemblages from the 

 Chalk at 840 and 810 feet depth (basal Cenomanian) in the Fetcham Mill bore. 

 Although a number of specimens were available for study, the majority proved 

 unsuitable as a result of distortion or unfortunate orientation : the figured specimen 

 was the only one capable of full study. It was thus not possible to confirm details 

 of the apical structure. 



Plate 1' is elongate and corresponds to the apical prolongation of the sulcus. At 

 least two other apical plates appear to be present : no anterior intercalary plate 

 could be distinguished. Six precingular and six postcingular plates are present ; 

 no posterior intercalary plate was distinguished. The antapex is occupied by a 

 single plate. 



The cingulum forms a strong laevorotatory spiral whose two ends differ in antero- 

 posterior position by three times its width. There appears to be no separation into 

 cingular plates. The sulcus is narrow and extends to the antapex. 



Fig. 36. Heliodinium voigti Alberti. Tabulation. Left, ventral view ; 

 right, dorsal view (plate 3" is missing). x c. 500. 



