n8 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Gonyaulacysta episoma sp. nov. 



PL 13, figs. 9, 10 ; Text-fig. 27 



Derivation of name. Greek, episomos, bulky, fat — referring to the rotund shell 

 shape. 



Diagnosis. A Gonyaulacysta with spherical to broadly ovoid shell with strong 

 apical horn of moderate length. Tabulation 4', ia, 6", ?5c, 6'", ip, 1 p. v., 1"". 

 Crests consisting of rows of thin spinelets connected distally by trabeculum ; 

 an extremely delicate membrane stretching between spinelets and trabecula. 

 Cingulum strongly spiral ; sulcus broad and short, stretching from about mid-point 

 on epitheca to about mid-point on hypotheca. Surface densely granular ; very few 

 spines occasionally present. Horn with trifurcate appearance produced by high 

 crest bounding plate 4'. 



Holotype. B.M.(N.H.) slide ¥.51730(1). Speeton Clay, Shell West Heslerton 

 Borehole No. 1, West Heslerton, Yorks., at 19-25 metres depth, Lower Cretaceous 

 (Upper Barremian). 



Dimensions. Holotype : overall length So[i, breadth 74^ ; shell length yo\L, 

 breadth 68[jl ; horn lOfx in length ; crests c.2jx in height ; cingulum c.3\i broad. 

 Range of dimensions : overall length 80-95^, horn length io-i8[jl, breadth 6o-8o[x. 



Description. An abundant species at this horizon, some 30 specimens having 

 been examined. All show some degree of distortion as a result of compression of 

 the originally spherical, fairly thin-walled shell. The horn is short, strongly tapering 

 and pointed ; it is tipped by plate 4', the high crest bounding this plate producing a 



Fig. 27. Gonyaulacysta episoma sp. nov. Tabulation. Left, ventral view 

 right, dorsal view. x c. 800. 



