MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 109 



Pluriarvalium Sarjeant 1962, from the Upper Jurassic of England, has the tabula- 

 tion 5', i-3a, 6", 6c, 6'", ip, ip.v., 1 — ?6p.c, 1"". It is characterized by possession 

 of a posterior circle of small plates surrounding the antapex. 



Glyphanodinium Drugg 1964, from the Paleocene of California, has the tabulation 

 ?i', 5", 6c, 6'", ip, ip.v., 1"". It is distinguished by the possession of only five 

 precingular plates and the lack of an anterior intercalary plate. 



There are in addition a number of genera whose tabulation is incompletely known 

 but which appear comparable to the Gonyaulax type. Eodinia Eisenack 1936, 

 from the Middle Jurassic of Germany, has a thick, porate wall and shows little sign 

 of tabulation ; there is no true cingulum, a helicoid suture being present instead. 

 Comparison to the Gonyaulax-type cysts is afforded by the overall shape and the 

 presence of an apical horn. 



Rhynchodiniopsis Deflandre 1935, from the Upper Cretaceous of France, has 

 raised, denticulate crests with spines arising at points of crest junction around the 

 transverse furrow. The surface is reticulate : the tabulation undetermined. In 

 shape and presence of an apical horn, it compares with the fossil cysts of Gonyaulax 

 type : there are no apparent distinguishing characters. 



Raphidodinium Deflandre 1936, from the Upper Cretaceous of France, has about a 

 dozen spines arising at crest nodes, these spines being of sufficient length to render 

 this a chorate cyst. Sutures are, however, present : the tabulation has not been 

 determined. 



Hystrichodinium Deflandre 1935, again from the Upper Cretaceous of France, is 

 another spinose form, the spines arising from sutures in considerably greater 

 numbers. The tabulation appears comparable to that of Gonyaulax but has 

 hitherto remained undetermined. 



Belodinium Cookson & Eisenack i960, from the Upper Jurassic of Australia, has a 

 circular cingulum, plates differentiated by raised crests, an apical horn and a " flat- 

 tened, membranous expansion " on the hypotract. This genus appears inadequately 

 characterized. This comment applies equally to Carpodinium Cookson & Eisenack 

 1962&, from the Lower Cretaceous of Australia whose tabulation is incompletely 

 known and whose other characters in no wise differ from those specified for Gonyaulax. 



Heliodinium Alberti 1961, from the Lower Cretaceous of Germany, resembles 

 Hystrichodinium but has flattened, dagger-like processes arising from the crests. 

 The tabulation is again undetermined but appears closely similar to that of Gonyau- 

 lax. 



There are thus a considerable number of genera of fossil dinoflagellates which 

 possess or approach the Gonyaulax tabulation pattern. Those forms directly allocated 

 to the genus Gonyaulax were originally considered to be the fossil remains of the 

 motile stage of that genera. It was nonetheless recognized that the shell wall 

 characteristically contained an opening of some kind, formed by median fission or by 

 loss of a plate or a group of plates. Following the demonstration by Evitt (1961) 

 that the occurrence of such openings (archaeopyles) indicated cysts, it became clear 



