166 MESOZOIC AND CAINOZOIC DINOFLAGELL ATE CYSTS 



Remarks. Superficially E. phragmites resembles Baltisphaeridium striolatum 

 Deflandre, the holotype of which was examined by one of the authors (R.J.D.) by 

 kind permission of Professor Deflandre. B. striolatum, however, has a definitely 

 striated periphragm on the surface of the central body and neither a distinctive apical 

 process nor an archaeopyle has been observed. It must be made clear, however, 

 that the holotype of B. striolatum is extremely dark and the lower surface, which may 

 possess an archaeopyle and an apical process, is not observable. 



OTHER SPECIES 



The following species are here included in Exochosphaeridium gen. nov. on the basis 

 of similarity in structure and process pattern : 



Exochosphaeridium palmatum (Deflandre & Courteville 1939). Upper Cretaceous ; 

 France. 



Exochosphaeridium striolatum (Deflandre 1937a). Upper Cretaceous ; France. 



The following species is tentatively referred to this genus, subject to subsequent 

 confirmation of the precingular position of the archeopyle : 



? Exoxhosphaeridium pseudhystrichodinium (Deflandre 19370). Upper Cretaceous ; 

 France. 



Genus CLEISTOSPHAERIDIUM nov. 



Derivation of name. Greek, kleistos, shut, closed ; sphaera, ball — in reference 

 to shell shape and the closed nature of the processes. 



Diagnosis. Chorate dinoflagellate cysts having spherical to ovoidal central 

 bodies bearing numerous processes, typically closed distally and without communica- 

 tion to endocoel. Number of processes typically exceeding 50 ; processes showing 

 no definite alignment, so that the tabulation is not determinable. Archaeopyle 

 apical, with zigzag margin. 



Type species. Cleistophaeridium diver sispinosum sp. nov. Eocene ; England. 



Remarks. It is not clear whether the processes of this genus are intertabular or 

 intratabular ; nor is there any differentiation between processes which would enable 

 the establishment of orientation. The shape and size of the archaeopyle, however, 

 strongly suggests that it is apical. 



All Mesozoic and Tertiary species, formerly attributed to Baltisphaeridium, which 

 show an apparent apical archaeopyle and which cannot be related to Surculosphaeri- 

 dium or Prolixosphaeridium, are provisionally reattributed to this genus. Species 

 are included whose process numbers are relatively low ; it is probable that re- 

 examination of these will necessitate their removal to other genera as soon as the 

 reflected tabulation is determined. 



