MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 213 



cingulum, but then the cingulum is by no means easily seen in the Speeton specimens. 

 It is therefore considered better not to propose a new name for these forms. 



Genus WETZELIELLA Eisenack 1938c : 186 

 IWetzeliella neocomica Gocht 



1957. IWetzeliella neocomica Gocht ; 172, pi. 19, figs. 1-4, pi. 20, figs. 4, 6, 7 ; text-figs. 7, 8, 



15, 16. 

 1 961. IWetzeliella neocomica Gocht ; Alberti : 11, pi. 4, figs. 17-19. 



Remarks. This species is represented by a number of poorly preserved specimens 

 from two horizons (Hauterivian, 99-25 and 103-25 metres depth) of the Speeton 

 Clay ; their dimensions fall within the range quoted by Gocht (overall length 72- 

 H7[x, breadth 50-94(1) but only one specimen (B.M.(N.H.) slide ¥.51715(1)) is 

 sufficiently well displayed to be measured in detail (overall length i03[x., breadth gojx). 

 The attribution of this species to the genus Wetzeliella was made with hesitation by 

 Gocht and must be considered doubtful, since archaeopyle formation is apical and 

 not intercalary as in typical species of that genus. However, the English specimens 

 are too poorly preserved to be used as bases for the erection of a new genus. 



It is probable that this species is related to Muderongia. Evitt (1961 : 397, pi. 8, 

 figs. 1, 2) has figured as " Form G " a species from the Lower Cretaceous Dilkuna 

 Formation of Pakistan which appears exactly intermediate between this latter genus 

 and 1W. neocomica. 



1 Wetzeliella neocomica was originally recorded from the Middle Hauterivian of 

 Germany (Gocht 1957). Alberti (1961) has recorded it from the Lower Hauterivian 

 to Upper Barremian of Germany, from the Hauterivian of Poland and Bulgaria and 

 from the Upper Cretaceous (Turonian and Coniacian) of Germany. The fact that it 

 has not yet been recorded from the Aptian, Albian or Cenomanian suggests that the 

 Upper Cretaceous specimens were reworked. 



CONCLUSIONS 



The known distribution of species of fossil dinoflagellate cysts in the five Speeton 

 Clay horizons examined, is shown in the accompanying Table. A striking feature 

 which emerges is the major change occurring in the Upper Barremian, when the 

 incoming of seven species combines with the disappearance of seven others to change 

 the whole character of the assemblage. The apparent change between the assemb- 

 lages from 99-25 metres depth (basal Upper Hauterivian) and 42-5 metres depth 

 (upper Lower Barremian) may be expected to fade out when intermediate assembla- 

 ges are examined. 



The 41 species listed in the table do not constitute the full array of dinoflagellate 

 cysts from these five horizons ; there remains a number of species present in low 

 numbers only and hitherto represented by damaged or obscured specimens, not 

 capable of full description. The Speeton assemblages as a whole are remarkably 

 rich and varied : it is clear that a number of species having a relatively limited 

 stratigraphic range will prove of considerable value as stratigraphic indices. 



