128 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



The cingulum forms a laevorotatory spiral such that its two ends differ in 

 antero-posterior position by almost 4 times its breadth. Six cingular plates are 

 present : the ends of plates ic and 6c extend somewhat into the sulcus. The 

 epitractal portion of the sulcus is of moderate breadth ; the hypotractal portion 

 broadens progressively as it approaches the antapex. 



A precingular archaeopyle is formed by loss of plate 3". 



Remarks. This species is based on a single specimen, well preserved and display- 

 ed : its characters are considered sufficiently distinctive to justify creation of a new 

 species. Shape, tabulation and crest character distinguish Gonyaulacysta whitei 

 sp. nov. from all other described species. 



Gonyaulacysta fetchamensis sp. nov. 

 PI. 15, figs. 1, 2 ; Text-fig. 33 



Derivation of name. Refers to the type locality, Fetcham Mill, Surrey. 



Diagnosis. A Gonyaulacysta having an ovoidal theca with strong, blunt apical 

 horn formed by periphragm only. Tabulation 3-?4', ia, 6", 6c, 7'", 2p, 1"" ; 

 sutures in form of low but well-marked, rather fibrous crests giving rise occasionally 

 to short, blunt spines. Cingulum narrow, strongly spiral ; sulcus broad, sunken. 

 Shell surface densely granular. 



Holotype. Geol. Surv. Colin, slide PF.3046(i). Chalk, H.M. Geological 

 Survey Borehole, Fetcham Mill, Surrey, at 840 feet depth. Upper Cretaceous 

 (basal Cenomanian). 



Dimensions. Holotype : overall length 12511, breadth io8[x ; shell length 95^, 

 breadth o,8fx ; length of horn c.25[x. 



Description. This species is extremely infrequent : of three specimens encoun- 

 tered, one (the holotype) is well preserved, the other two are severely damaged. 



The shell is broadly ovoidal, giving rise to a strong, blunt apical horn ; this horn is 

 formed by the periphragm only and constitutes what is effectively an apical pericoel. 

 There are certainly three and possibly four apical plates, presence of a crest separating 

 plates 3' and 4' being unconfirmed. Plate 1' is unusually large and club-shaped. 

 Six precingular plates are present, with plate 6" reduced to accommodate a sub- 

 triangular anterior intercalary plate. Seven post cingular plates are present. 

 Plates 1'" and 2'" are reduced to accommodate a large posterior intercalary plate, and 

 plate 7'" is also reduced to accommodate a second, smaller intercalary plate. (The 

 crest separating plates 5'" and 6'" is somewhat torn.) The antapex is occupied by a 

 single plate of moderate size. 



The cingulum is narrow, forming a laevorotatory spiral such that its two ends 

 differ in antero-posterior position by almost three times its width. The ends of the 

 cingulum are widely separated by a very broad sulcus, which widens further in its 

 posterior portion. 



