MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS in 



A. Genera with precingular archaeopyle 



Genus GONYAULACYSTA Deflandre 1964 : 5 



Emended diagnosis. Proximate dinoflagellate cysts, spherical, ovoidal, ellip- 

 soidal or polyhedral, with the tabulation 3-4', o-ia, 6", 6c, 6'", ip, 0-1 p. v., 1"". 

 Cingulum strongly or weakly helicoid. Cingular plates (6c) well or poorly marked ; 

 ventral surface may show division into additional small plates. Sulcus generally 

 but not constantly extending onto epitract. Apical horn frequently, but not 

 constantly present ; median and antapical horns lacking. Sutures in form of low 

 ridges ; bearing crests of varied form (smooth denticulate or spinous ; perforate or 

 imperforate) ; or marked by lines of spines of varied form. Height of spines or 

 crests always less than \ of shell width. A precingular archaeopyle formed by loss 

 of plate 3". (Archaeopyle not always present.) Surface smooth, granular, nodose, 

 punctate or reticulate. 



Type species. Gonyaulax jurassica Deflandre 1938. Upper Jurassic (Oxford- 

 ian) ; France. 



Remarks. The generic diagnosis is emended to include reference to tabulation 

 and to exclude forms characterized by very high crests, very long sutural spines, or a 

 general spine cover. Forms with high crests are referred to Heslerlonia gen. nov. ; 

 forms with long sutural spines to Heliodinium, Hystrichodinium or Raphidodinium : 

 and forms with a general spine cover to Acanthogonyaulax. Forms according to this 

 diagnosis but with an apical archaeopyle are referred to Meiourogonyaulax ; forms 

 with an epitractal archaeopyle to Rhaetogonyaulax and Dichadogonyaulax ; and 

 forms with a cingular archaeopyle to Ctenidodinhim. 



Gonyaulacysta gongylos sp. nov. 



PL 13 figs. 1, 2 ; Text-fig. 23. 



1961. Gonyaulax sp., Sarjeant : 97, pi. 13, fig. 15 ; text-fig. 6. 



Derivation of name. Greek, gongylos, ball, in reference to the spherical shape. 



Diagnosis. A Gonyaulacysta having an almost spherical theca, with short blunt 

 apical horn. Tabulation 4', ia, 6", 7c, 6'", ip, 1"" ; plate boundaries usually 

 bearing low, denticulate crests, Plate 1' elongate and corresponding to anterior 

 prolongation of sulcus ; plate 4' very small, occupying horn tip. Plate 1'" reduced 

 and elongate ; its boundary with sulcus not marked by a crest. Sulcus and cingu- 

 lum both relatively broad ; cingular plate 7c small and pentagonal in shape. 



Holotype. B.M.(N.H.) slide ¥.51708(2). Lowest Oxford Clay ; Castle Cliff, 

 Scarborough, Yorks. Upper Jurassic (Lower Oxfordian). 



Dimensions. Holotype : overall length 47(a, length of horn 5[x ; overall breadth 

 45pt. ; breadth of cingulum c. 5[x. The few other specimens seen proved too severely 

 damaged for measurement, but appear of comparable dimensions. 



