MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 9 



described, from all stratigraphic levels in the Mesozoic and Cainozoic, is reviewed and generic 

 transfers are proposed where necessary. The resultant picture of the stratigraphic distribution 

 of genera and species emphasizes the value of these microfossils as stratigraphic indices. 



I. INTRODUCTION 



During the last few years, research into the nature and distribution of fossil dino- 

 flagellate cysts has been very active, stimulated by realization of the potential value 

 of these microfossils in the correlation of marine strata and by their biological 

 interest. The great bulk of recent researches has been made by French and German 

 palynologists, notably Deflandre, Valensi, Eisenack and Gocht. 



In Britain, a brief period of interest followed Ehrenberg's initial discovery of these 

 fossils in flints and his visit to England in 1838: however, after 1850, no further 

 attention was paid to these fossils for a century. In 1957 Downie described a number 

 of types from the Upper Kimmeridge Clay (Kimmeridgian) : this was the first study 

 of British Jurassic dinoflagellates. Subsequently Sarjeant, in a series of publications, 

 has described assemblages from the Cornbrash, Oxford Clay, Corallian and Ampthill 

 Clay (Callovian to Oxfordian) : species described by this author (1962) from the 

 Cotham Beds (Rhaetic) include the earliest known clearly tabulate cysts. The 

 distribution of dinoflagellate cysts in the Lias has been studied by Wall (1965). 



The first British Lower Cretaceous assemblage to be described was from the 

 Hauterivian section of the Speeton Clay (Neale & Sarjeant 1962), species from other 

 levels of the Speeton Clay are described herein. An assemblage from the Cambridge 

 Greensand (Middle Cretaceous) has been described by Cookson & Hughes (1964). 

 Since 1850, no further work has been published on the Upper Cretaceous : the first 

 results of studies by Davey, at present in progress, are included in the present work. 



No British Tertiary assemblages have yet been described. Dinoflagellate cysts 

 from the London Clay (Eocene) have been mentioned by Eagar & Sarjeant (1963) 

 and figured by Macko (1963), but the first extended study was that made by G. L. 

 Williams (thesis, 1964), of which results are given herein. 



No Quaternary assemblages have been described ; work by Deflandre referred to 

 by West (1961) has not been published. 



There has been considerable progress in recent years in our understanding of the 

 nature of these cysts, largely as a result of the studies of Evitt (1961, 1963, Evitt & 

 Davidson 1964). He has elucidated some of their fundamental structures and drawn 

 attention to the importance of the cyst openings (archaeopyles) and of structures 

 representing a reflected tabulation, thus effectively demonstrating the affinity of 

 many formerly problematic genera (the " hystrichospheres " sensu stricto). 



This paper comprises a full-scale review of certain of the principal genera of fossil 

 dinoflagellate cysts, involving extensive revision of generic diagnoses and the 

 erection of new taxa. In addition, new genera and species are described from 

 various Mesozoic and Tertiary horizons. 



