PRESENT TAXONOMIC ATTRIBUTIONS 

 OF THE DINOFLAGELLATE CYSTS AND 



ACRITARCHS 



TREATED BY DAVEY, DOWNIE, 

 SARJEANT AND WILLIAMS (1966, 1969) 



By LINDA A. KRUKEWICH and WILLIAM A. S. SARJEANT 



INTRODUCTION 



The major work here reprinted marked the beginning of a new epoch in systematic 

 work on fossil dinoflagellate cysts, in that it embodied not only the first attempt 

 to formulate a separate morphological terminology for these microfossils but also 

 the first extensive application of the ideas of Evitt (1961, 1963), that archaeopyle 

 character and process shape and distribution could be used as prime criteria in 

 taxonomy. 



In the seventeen years that have elapsed since its publication, there has been a 

 further explosive expansion in our observation and comprehension of fossil dino- 

 flagellate cysts, with a consequent expansion of terminology (see Evitt et al. 1967, 

 William, Sarjeant & Kidson 1978, Sarjeant 1982a). The importance in taxonomy 

 of such additional characters as the shape of process terminations and the direc- 

 tion of their branches, the exact shape of the archaeopyle, the presence and 

 pattern of minute plates (we would now style them "paraplates") in the mid- 

 ventral region, and the exact relationships of the anterior ventral plates has come 

 to be recognized (see for example Evitt 1967, Lentin & Williams 1976, Sarjeant, 

 1982b). In contrast, some features - for example, the presence of an ectophragm 

 - are now considered less reliable as means for the separation of taxa. The result 

 has been the reassignment to other genera of many of the species mentioned in 

 the 1966 paper and its first Appendix (1969). The diagnoses of many of these 

 genera and species have been greatly modified, a few taxa have been rejected as 

 junior synonyms and some species, then treated as acritarchs, are now recognized 

 to be dinoflagellate cysts. 



To simplify understanding of the present taxonomic situation, a checklist is 

 here appended in which the names of all genera and species mentioned in 1966 

 and in the 1969 Appendix are given in alphabetical order. Any revisions to their 

 diagnoses are noted; and the present names, where different to those cited earlier, 

 are indicated. Where their taxonomic allocation remains a matter for controversy, 

 the alternative ideas are noted. The species placed in 1966 into the acritarch genus 

 Baltisphaeridium are included in proper alphabetical position; if these are still 

 considered to be acritarchs, that fact is likewise noted. Where taxa appeared 

 under different generic names in 1966 and 1969, both names are included in the 

 list. A full reference section, citing all papers referred to in the list, is appended. 



