152 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Genus GLYPHANODINIUM Drugg 1964 



Type species. Glyphanodinium facetum Drugg 1964. Palaeocene (Danian) ; 

 California, U.S.A. 



Remarks. This is a genus of distinctive proximate dinoflagellate cysts of pentago- 

 nal shape, with the tabulation ?i', oa, 6c, 6'", ip, 1 p. v., 1"", the archaeopyle being 

 formed by loss of the single (?) apical plate. The cingulum is situated high on the 

 test, the epitract being thus small, the hypotract large. The overall shell size is 

 small. It differs from Meiourogonyaulax in the apparent number of apical plates, 

 and from Microdinium in overall shape and the presence of only five precingular 

 plates. 



Genus EISENACKIA Deflandre & Cookson 1955 : 258 



1954. Eisenackia Deflandre & Cookson : 1236 (name only). 



Emended diagnosis. Proximate dinoflagellate cysts, spheroidal or ovoidal in 

 shape, with the tabulation 2-3', 6", ?6c, 6'", 2p, 1"" ; additional plates occupy 

 ventral area, there being no sulcus as such. Plates consisting of raised areas of shell 

 surface, isolated frcm one another by pattern of " channels " corresponding in 

 position to sutures. (It is here proposed that such inverse equivalents of sutures be 

 termed " fossae ".) Cingulum weakly helicoid. Shell surface typically reticulate, 

 possibly also granular or punctate. Apical archaeopyle formed by loss of apical 

 plates. 



Type species. Eisenackia crassitabulata Deflandre & Cookson 1955. Paleocene 

 to Lower Eocene ; Australia. 



Remarks. The diagnosis is emended to stress the characteristic form of the 

 tabulation, as plates separated by fossae, and to include reference to the mode of 

 archaeopyle formation. The latter character was remarked on by Deflandre & 

 Cookson (1955 : 260) in the description of the type species. 



C. Genera with epitractal archaeopyle 

 Genus RHAETOGONYA ULAX nov. 



Derivation of name. Refers to the occurrence of the type species in the Rhae- 

 tian (Rhaetic) Stage, uppermost Triassic, and to possession of a Gonyaulax type of 

 tabulation. 



Diagnosis. Proximate dinoflagellate cysts, spindle-shaped or biconical, typically 

 with the tabulation 4', ia, 6", 6'", ip, 1"" : tabulation well or poorly marked by 

 ridges or partially or entirely indeterminable. Cingulum strongly or weakly spiral, 

 laevorotatory, divided into plates (?6c) or without such division. Surface smooth, 

 granular, nodose, punctate or reticulate ; ornamentation may mask the tabulation. 

 Archaeopyle (where present) epitractal, formed by schism of shell immediately 

 anterior to cingulum. 



