8 APPENDIX TO "STUDIES ON MESOZOIC 



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

 soidal or polyhedral, with an apical horn and the reflected tabulation 3-4', o-ia, 6", 

 6c, 5-6"', 1 p, 0-1 p. v., 1"", o-xs. Cingulum strongly or weakly helicoid ; cingular 

 plates well or poorly marked. Sulcus generally but not constantly extending on to 

 the epitract ; undivided or subdivided into a variable number of small plates. 

 Apical horn typically formed from the periphragm only, less frequently from both 

 shell layers ; rarely, an apical or antapical pericoel is present (but not both), but the 

 two layers are most often otherwise in continuous contact. Median and antapical 

 horns lacking. Sutures marked by 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 J of shell width. 

 A precingular single-plate archaeopyle, formed by loss of plate 3", is developed, the 

 operculum typically becoming wholly detached : in some individual specimens, the 

 archaeopyle may not be developed. Surface of periphragm smooth, granular, 

 nodose, punctate or reticulate ; forms with a general spine cover are excluded. 



Type species. Gonyaulacysta jurassica (Defiandre) Norris & Sarjeant, 1965 

 =Gonyaulax jurassica Defiandre, 1938 ; 168-70, pi. 6 figs. 2-5, text-figs. 1-2. 

 Upper Jurassic (Oxfordian), France. 



Remarks. The diagnosis is emended to include the presence of an apical horn, 

 formed by an outbulge of the periphragm or of both shell layers, as an essential 

 characteristic. Species in which an apical prominence is developed merely from the 

 junction of crests, such as Leptodinium freakei (Sarjeant) Sarjeant and Leptodinium 

 millioudi (Sarjeant) Sarjeant, are excluded, as are species with a general spine cover 

 or with especially long sutural spines (see discussion in Sarjeant, 1966b ; 111). 

 Species having an apical or epitractal archaeopyle, species having a precingular 

 archaeopyle formed by the loss of the equivalent of more than one plate, and species 

 having a combination archaeopyle are excluded. The currently known range of the 

 genus is Middle Jurassic — Miocene. 



Other species. 

 Gonyaulacysta aculeata (Klement) Sarjeant, comb, nov., =Gonyaulax aculeata 



Klement, i960 ; 42-4, pi. 5 figs. 6-9, text-fig. 21. Upper Jurassic, Germany. 

 Gonyaulacysta aichmetes Sarjeant, 1966b ; 123-4, pi- I 3 n g s - 5 _ 6, text-fig. 30. 



Lower Cretaceous, England. 

 Gonyaulacysta ambigua (Defiandre) Sarjeant, comb. nov. =Gonyaulax ambigua 



Defiandre, 1939 ; 144, pi. 6 fig. 2. Upper Jurassic, France. 

 (Note : The indirect citation of Deflandre's paper in Sarjeant 1968, does not 



conform to Art. 33 para. 3 and note 1 of the ' I. C.B.N.'. The new combination 



is, therefore, here reproposed.) 

 Gonyaulacysta apionis (Cookson & Eisenack) Sarjeant, comb, nov., =Gonyaulax 



apionis Cookson & Eisenack, 1958 ; 36, pi. 3 fig. 7, text-figs. 3-4. Lower 



Cretaceous, Australia. 

 Gonyaulacysta axicerastes Sarjeant, 1966b ; 114-6, pi. 13 figs. 11-12, text-fig. 



25. Lower Cretaceous, England. 



