MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



205 



Apteodinium maculatum Eisenack & Cookson 

 PL 22, fig. i ; Text-fig. 54 



i960. Apteodinium. maculatum Cookson & Eisenack : 4, pi. 2, figs. 1-3. 



Remarks. This species, hitherto recorded only from the Lower Cretaceous (Aptian 

 to Albian) of Australia, occurs in low numbers in the assemblages from the Shell 

 West Heslerton Borehole, West Heslerton, Yorkshire, at 42-50 metres depth. 

 (Lower Barremian). 



The English specimens are somewhat smaller than the Australian type material : 

 the figured specimen (B.M.(N.H.) slide ¥.51718(4)), with overall length 75[x, breadth 

 64^, falls a little below the quoted Australian range of length 74-105^, breadth 

 70-105(1. There are faint indications of a sulcus and the " small thickened areas with 

 circular outlines " noted by Eisenack and Cookson are totally lacking. Nor has an 

 archaeopyle been observed to date. (The " hoof-shaped pylome " mentioned by 

 those authors must be interpreted as a precingular archaeopyle.) However, the 

 triviality of these differences and the complete correspondence in other characters 

 does not justify any nomenclatural distinction of the English specimens, which 

 accordingly represent a considerable extension in the geographic and stratigraphic 

 range of this species. 



Genus DOIDYX nov. 



Derivation of name. Greek, doidyx, pestle, in reference to the shell shape. 



Diagnosis. Proximate dinoflagellate cysts with flattened biconical shell, pro- 

 nouncedly asymmetical. Epitract in form of high cone which may be drawn out 

 into an apical horn, giving a mammillate appearance : hypotract in form of flattened 

 cone, with or without antapical prominence. Shell bulging out laterally to one side 

 more than to the other ; lateral horns lacking. Greater part of shell surface covered 



Fig. 54. Apteodinium maculatum Eisenack & Cookson, showing the dense granulosity 

 and the positions of cingulum and sulcus. x c. 800. 



