130 MESOZOIC AND CAINOZOIC DINOFLAGELL ATE CYSTS 



The crests are fibrous in nature, with close-set slits in places : they give rise to 

 occasional short spines. In the holotype a broken line of " tubercles ", like an 

 embryonic crest, crosses plate 5" ; this was not observed in the other specimens. 



A precingular archaeopyle is formed by loss of the large plate 3". In the holotype, 

 the region round the archaeopyle is somewhat folded. 



Remarks. The generic allocation of Gonyaulacysta fetchamensis is questionable, 

 in view of its possession of two posterior intercalary plates and a seventh postcingular 

 plate. The similarity in general morphology to a number of Lower Cretaceous 

 species of Gonyaulacysta resulted in its allocation to that genus ; however, it may 

 subsequently prove preferable to erect a new genus for species having this tabulation 

 pattern, a procedure not now adopted in view of the low numbers of specimens en- 

 countered to date. 



The most closely comparable species is undoubtedly Gonyaulacysta orthoceras 

 (Eisenack), which has a similar general form and apical horn. However, Gonyaulax 

 fetchamensis is clearly distinguished by the form of its crests and the detail of ventral 

 tabulation. 



OTHER SPECIES 



The following species are here attributed to the genus Gonyaulacysta on the basis 

 of general structure and formation of an archaeopyle by loss of plate 3" : 



Gonyaulacysta aculeata (Klement i960). Upper Jurassic (POxfordian-Kimmerid- 

 gian) ; Germany. 



Gonyaulacysta amabilis (Deflandre 1939). Upper Jurassic (Kimmeridgian) 

 France. 



Gonyaulacysta ambigua (Deflandre 1939). Upper Jurassic (Kimmeridgian) 

 France. 



Gonyaulacysta apionis (Cookson & Eisenack 1958). Lower Cretaceous (Albian) 

 South Australia. 



Gonyaulacysta aptiana (Deflandre 1935). Lower Cretaceous (Aptian) ; France 



(see p. 140). 

 Gonyaulacysta cladophora (Deflandre 1938). Upper Jurassic (Oxfordian) ; France. 



Gonyaulacysta clathrata (Cookson & Eisenack 19606). Upper Jurassic (PTithonian) ; 

 Western Australia. 



Gonyaulacysta crassicornuta (Klement i960). Upper Jurassic (Kimmeridgian) ; 



Germany. 

 Gonyaulacysta cretacea (Neale & Sarjeant i960). Lower Cretaceous (Hauterivian) ; 



England. 



Gonyaulacysta diaphanis (Cookson & Eisenack 1958). Cretaceous (? Aptian) ; 

 Western Australia. 



Gonyaulacysta edwardsi (Cookson & Eisenack 1958). Cretaceous (Aptian- 

 Turonian) ; Australia. 



