[46 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



From the angular profile of the apical archaeopyle, the former presence of at least 

 four apical plates is deduced. There is no anterior intercalary plate. Six precingu- 

 lar plates are present, plate 6" being slightly reduced. Six postcingular plates are 

 present, plate 1'" being reduced and elongate, separated from the antapex by a 

 moderately large posterior intercalary plate. The antapex is occupied by a single 

 large plate and is separated from the sulcus by a quadrate posterior ventral plate. 



The cingulum forms a strong laevorotatory spiral such that its two ends differ in 

 antero-posterior position by over twice its width. It is clearly subdivided into six 

 cingular plates. The sulcus is roughly wedge-shaped, broadening towards the 

 posterior ; it bears low ridges forming an irregular pattern. 



The shell surface is alveolar to punctate. The crests are moderately high, faintly 

 striate and intermittently perforated ; their distal edges are in part smooth, in part 

 finely denticulate. Crest nodes are strengthened by stout spines in some or all 

 cases. The crests bordering the sulcus are very reduced. 



Remarks. Professor Georges Deflandre permitted the author and Mr. R. J. 

 Davey to examine the holotype during visits to Paris, and also provided the photo- 

 graph ; his courtesy is gratefully acknowledged. 



Meiourogonyaulax valensii sp. nov. is distinguished from the other species of this 

 genus in the detail of tabulation and the nature of the crests. 



OTHER SPECIES 



The following species are here attributed to Meiourogonyaulax gen. nov. and accord 

 with the diagnosis of this genus : 



Meiourogonyaulax bulloidea (Cookson & Eisenack 19606). Upper Jurassic 

 (PTithonian) ; Western Australia. 



Meiourogonyaulax cristulata (Sarjeant 1959). Middle Jurassic (Callovian) ; 



England. 

 A third species is doubtfully attributed to the genus : 



? Meiourogonyaulax caytonensis (Sarjeant 1959). Middle Jurassic (Callovian) ; 

 England. 



The mode of archaeopyle formation in this latter species is not clear. The holotype 

 has an intact apex, but lacks plate 2", suggesting a precingular archaeopyle in a 

 unique position : other specimens lack an apex. Assignment to Meiourogonyaulax 

 is thus provisional. 



Genus XIPHOPHORIDIUM nov. 



Derivation of name. Greek, xiphos, sword : phor-, suffix meaning to bear, 

 carry. 



Diagnosis. Proximo-chorate dinoflagellate cysts, spheroidal to ovoidal or 

 polygonal withtabulation ?4', ia, 6", o-ip, 6'", 1"". Cingulum strongly or weakly 



