i 4 o MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



In absence of full knowledge of the tabulation, the above diagnosis includes no 

 characters, save possibly the posterior widening of the sulcus, which distinguish it 

 from Gonyaulax, as accepted at the time of publication, or from Gonyaulacysta as 

 defined by Deflandre and here redefined. The status of this genus must be regarded 

 as questionable. 



[Genus RHYNCHODINIOPSIS Deflandre 1935] 



Type species. Rhynchodiniopsis aptiana Deflandre 1935. Lower Cretaceous 

 (Aptian) ; France. 



Remarks. In his first full description of this genus (1936a : 32), Deflandre 

 remarks on its apparent close relationship to Gonyaulax. Examination of his 

 excellent figures suggests the tabulation 4~?5', ?ia, 6", 6g, 6'", ip, 1"" ; a pre- 

 cingular archaeopyle is present, formed by loss of plate 3". Three distinguishing 

 characteristics are cited by Deflandre — the presence of a strong, hollow, apical horn ; 

 the presence of denticulate, aliform crests on sutures ; and the presence of strong 

 curved spines arising from crest nodes along the edges of the cingulum. The first 

 two characters are shared by many species of Gonyaulacysta ; the figures indeed 

 strongly suggest a close affinity to Gonyaulacysta jurassica. The third distinguishing 

 character does not alone warrant separation to generic level. 



It is considered that this genus was, at the time of its publication, effectively a 

 junior homonym of Gonyaulax, none of the characters cited warranting the creation 

 of a new name. It is therefore proposed that the name Rhynchodiniopsis be aband- 

 oned and the single species, R. aptiana, from the Lower Cretaceous (Aptian) of 

 France, be transferred to Gonyaulacysta. 



Genus HYSTRICHODINIUM Deflandre 1935 : 229 



Emended diagnosis. Proximo-chorate dinoflagellate cysts, spheroidal, ovoidal 

 or polygonal in shape. Tabulation in general accord with Gonyaulax pattern, but 

 not determined in detail. Long, hollow spines, rounded in cross-section and fairly 

 stiff, arising from positions of plate boundaries : plate boundaries otherwise marked 

 by low crests or not at all. Cingulum strongly or weakly helicoid, well-marked ; 

 sulcus poorly marked. Length of spines variable, but typically exceeding \ of shell 

 width. Shell surface smooth, granular, punctate, nodose or areolate. A precingular 

 archaeopyle formed, presumably by loss of plate 3". 



Type species. Hystrichodinium pulchrum Deflandre 1935. Upper Cretaceous ; 

 France. 



