. Bulletin of the British Museum (Natural History), Geology. 258 DINOFLAGELLATE CYSTS AND ACRITARCHS Gonyaulacysta cf. helicoidea (Eisenack & Cookson) (PI. 2, figs, i, 2; Text-fig. 11) Description. An almost spherical theca with a short and broad, blunt apical horn. Tabulation : 4', ia, 6", 6c, 6" ', ip and 1" ". Denticulate crests rise up from the plate boundaries ; the height and character of denticulation are variable. The strongly spiral cingulum separates the epitract and the hypotract, which are almost equal in size. Sulcus sigmoidal. Surface of the shell tubercul
. Bulletin of the British Museum (Natural History), Geology. 258 DINOFLAGELLATE CYSTS AND ACRITARCHS Gonyaulacysta cf. helicoidea (Eisenack & Cookson) (PI. 2, figs, i, 2; Text-fig. 11) Description. An almost spherical theca with a short and broad, blunt apical horn. Tabulation : 4', ia, 6", 6c, 6" ', ip and 1" ". Denticulate crests rise up from the plate boundaries ; the height and character of denticulation are variable. The strongly spiral cingulum separates the epitract and the hypotract, which are almost equal in size. Sulcus sigmoidal. Surface of the shell tuberculate ; scattering of the tubercules irregular. Precingular archaeopyle forms by loss of plate 3". Figured specimen. BM(NH) slide ¥.53931(1). Clay from the Liostrea delta Bed of Villerville, Normandy (VN 184). Dimensions. Figured specimen : overall length 45 /x, breadth 40 it ; horn length 5 /jl. Holotype dimensions (given by Eisenack and Cookson) are length 78/x, breadth. Fig. 11. Gonyaulacysta cf. helicoidea (Eisenack & Cookson). Tabulation, view ; right, dorsal view. xc. 1360. Left, ventral 56/x. Range of English specimens (as quoted by Sarjeant) : overall length 44-53 /x, breadth 42-46 /x. Remarks. G. helicoidea was originally recorded from the Lower Cretaceous (Aptian or older) of South Australia by Eisenack and Cookson (i960) ; subsequently Sarjeant observed it in the Speeton Clay of England (Lower Barremian), emended the diagnosis, and gave an exact tabulation of the species (1966). It was also observed in the Barremian of Russia by Vozzhennikova (1967). A single, excellently preserved specimen was recorded from the basal Kimmeridgian of Normandy. This specimen is closely comparable with the specimen figured by Sarjeant ; the only difference is in the height of the apical horn (although it has been mentioned that the length of the horn is very variable, by Sarjeant, 1966c). Dimen-. Please note that these images are extracted from scanned page images that may have
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