34 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Holotype. Slide " Feuerstein von Delitzsch, no. XXV " of Ehrenberg (ringed 

 in white on the third slice of flint). Lodged at the Institut fur Palaontologie und 

 Museum der Humboldt-Universitat, Berlin. Upper Cretaceous ; Germany. 



Dimensions. Holotype : diameter of central body 42 by 48^, length of processes 

 I3~25(j.. Range of Lower Cretaceous (Barremian) specimens : diameter of central 

 body 34-41^, length of processes 5-i3[x. Number of specimens measured, 2. Range 

 of Cenomanian specimens ; diameter of central body 30-50^, length of processes 

 7— 27JX. Number of specimens measured, 13. Range of London Clay (Ypresian) 

 specimens ; diameter of central body 32-56{i., length of processes ii-20[jl. Number 

 of specimens measured, 9. 



Description. The plates of the cingulum are distinctive, being elongate and 

 six-sided. There are two gonal processes between adjacent cingular plates and 

 these are usually connected by a well developed membrane. The longitudinal 

 furrow is obvious and is considerably larger on the hypotract. A distinctive simple 

 apical process is commonly present. When the trapezoid precingular archaeopyle is 

 present it is noticeable that the margin appears to lie just within the boundary of 

 plate 3". One specimen of H. ramosa var. raniosa (PI. 3, fig. 1) has been observed in 

 the Upper Oxfordian (Throstler Clay, Upper Calcareous Grit) of England (Sarjeant 

 i960). The specimen is large (central body diameter 58 by 61 jx, length of processes 

 up to I9[x) but otherwise appears to be typical of this variety. 



This variety has a known stratigraphic range from the Middle Barremian to the 

 Ypresian. 



Remarks. H. ramosa var. ramosa is characterized by the form of its processes 

 and the absence or scarcity of sutural processes. Doubtful descriptions or illustra- 

 tions of forms classified as H. furcata or H. ramosa have not been included in the 

 synonymy of H. ramosa var. ramosa and are placed in H. ramosa (Ehrenberg) var. 

 indet. The varieties of H. furcata described by Rossignol (1964) must be transferred 

 to H. ramosa. 



Hystrichosphaera ramosa var. gracilis nov. 

 PL 1, fig. 5 ; PL 5. fig- 6 



1955. Hystrichosphaera ramosa (Ehr.) ; Deflandre & Cookson : 263, pi. 5, fig. 8. 

 1963. Hystrichosphaera ramosa (Ehr.) ; G6rka : 48, pi. 6, figs. 6, 7. 



Derivation of name. Latin, gracilis, slender or graceful — with reference to the 

 slender, rather delicate processes. 



Diagnosis. A variety of H. ramosa (Ehrenberg) with smooth, thin-walled central 

 body bearing gonal and sutural processes. Processes solid or hollow and relatively 

 long and slender. Crests proximal and extending along all processes often as far as 

 the trifurcation. Gonal processes mainly trifurcate, sutural processes bifurcate, all 

 but smallest terminating with small trifurcation. 



