H2 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Descriptions. Theca almost spherical, but having a somewhat polygonal 

 appearance because of the angularly set crests. The horn is tipped by plate 4' ; 

 extensions of plates 1-3' form its base. The anterior intercalary plate, ia, is 

 quadrate and separated from the horn by plate 3'. Of the six precingular plates, 

 plate 6" is reduced, plate 3" notably large and forming the anterior dorsal surface. 

 It is arguable whether there are five or six postcingular plates, since plate 1'" is 

 defined only by the angles formed by plates 2'" and ip with the furrow and sulcus. 

 Plate 3'" is large and forms the posterior dorsal surface : plate 2" is reduced to accom- 

 modate the quadrate posterior intercalary plate. The antapex is occupied by a 

 single polygonal plate. 



The cingulum is broad and laevorotatory, its two ends differing in antero-posterior 

 position by the cingulum's width. A pentagonal plate is present between the sulcus 

 and the more posterior end of the cingulum ; this is here designated plate 7c, but 

 since its form does not correspond with that of the other cingular plates, a special 

 name might be merited. The sulcus is narrow in its anterior portion, broadening to 

 contact with the cingulum and thenceforward remaining of constant breadth in its 

 posterior portion. 



The surface of the periphragm is generally smooth, but bears a sparse scatter of 

 coarse granules. The crests are strong but low, with well marked denticulations, 

 resembling in form crest type f. of Gonyaulacysta jurassica (cf. Sarjeant, 1961, 

 text-fig. 1). 



Remarks. Gonyaulacysta gongylos sp. nov. is an unusually small species character- 

 ized by its overall shape, its apical tabulation, and the presence of plate jg. Re- 

 examination of the holotype under a more powerful microscope has led to a fuller 

 elucidation of the structure, in particular with regard to the crest form and the 

 pattern of postcingular plates (a presumed plate boundary being shown to be merely 

 a fold). 



Fig. 23. Gonyaulacysta gongylos sp. nov. Tabulation. 



view. X c. 800. 



Left, ventral view ; right, dorsal 



