MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



113 



This species remains infrequent, only a very few severely damaged specimens 

 having been encountered subsequently. For this reason also, the character of the 

 archaeopyle remains to be confirmed ; allocation to Gonyaulacysta is made on the 

 basis of tabulation and general morphology. It shows a similarity to a group of 

 Upper Jurassic-Lower Cretaceous species Gonyaulacysta jurassica, G. eisenacki, 

 G. cretacea and G. helicoidea) in crest form and in the reduction of plate 1", but 

 differs from them in shape and presence of plate 7c. 



Gonyaulacysta palla sp. nov. 

 PI. 13, figs. 3, 4 ; Text-fig. 24 



Derivation of name. Greek, palla, ball, in reference to the overall shape. 



Diagnosis. A Gonyaulacysta with almost spherical theca and prominent apical 

 horn. Tabulation 4', ia, 6", ?6c, ?7'", ip, 1"" ; plate boundaries demarcated by 

 crests formed of very short spines arising from low ridges. Plate 1' elongate, 

 occupying anterior prolongation of sulcus and relatively large ; plate 4' small, 

 occupying horn tip. Sulcus and cingulum of moderate breadth. Plate 1'" small 

 and quadrate : posterior intercalary plate correspondingly small. Plate 2'" some- 

 what larger than plate 1'", but remaining markedly smaller than other postcingular 

 plates. Number of postcingular plates probably seven, but presence of crest 

 between plates 4'" and 5'" not confirmed. 



Holotype. B.M.(N.H.) slide ¥.51718(2). Speeton Clay, Shell West Heslerton 

 Borehole No. 1, West Heslerton, Yorks., at 42-50 metres depth. Lower Cretaceous 

 (Lower Barremian) . 



Dimensions. Holotype : overall length 62[i, length of horn, iojx ; overall 

 breadth $o\x ; breadth of cingulum c.4(x. Range of dimensions observed ; overall 

 lengths 60-64^, overall breadths 46-52^. 



Fig. 24. Gonyaulacysta palla sp. nov. Tabulation. Left, ventral view ; 

 right, dorsal view. x c. 800. 



