MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 31 



processes are trifurcate but some of the processes occupying a medial position are 

 shown to be bifurcate. Some of the trifurcate processes possess small terminal 

 bifurcations, and the membranes are always shown to be proximal. The number of 

 processes is said to be approximately 40. Unfortunately, H. furcata was not 

 similarly treated, Lejeune having apparently failed to recognize any of the original 

 specimens figured by Ehrenberg as Xanthidium furcatum Ehrenberg. 



Valensi (1955) described forms in which the processes terminate in two small 

 spines or a fork. However his figures do not always correspond to the description 

 given. Some of the processes are open with serrate lips and others are trifurcate with 

 distal bifurcations. Some of the specimens have prominent crests with elevated 

 membranes and differ from both of Ehrenberg's forms. 



Eisenack (1958) described specimens attributed to H. furcata from the Aptian of 

 Germany having short, thick processes with broad bases and dividing into two or 

 three spines distally. In his description he emphasized the wide degree of variation 

 in the species as interpreted by earlier workers. 



Maier (1959) described and figured H. furcata from the Miocene of Germany, her 

 forms possessing solid processes which divide distally in two to four spines. Gocht 

 (1959) described specimens of H. furcata from the Neocomian of Germany as some- 

 times having isolated processes while others possessed well developed membranes 

 along the plate boundaries uniting adjacent processes. H. ramosa, as described by 

 Gerlach (1961), from the German Oligocene, possesses oval central bodies and 

 trifurcate processes which are bifurcate distally. 



Brosius (1963) restricted H. furcata to forms with bifurcate and trifurcate processes 

 and H. ramosa to those with trifurcate processes, each furcation terminating in a 

 short bifurcation. Cookson & Hughes (1964) had difficulty in identifying H. 

 ramosa in the Albian/Cenomanian of Cambridge and distinguished it from H. furcata 

 by its larger size, thicker-walled processes, more strongly outlined fields and more 

 pronounced membranes. 



Since the two species were first figured by Ehrenberg, there has been considerable 

 difference of opinion as to how each species should be diagnosed, and subsequent 

 authors appear to have attributed their specimens somewhat randomly to one, or more 

 rarely, to both species. As Lejeune (1937) first pointed out with reference to these 

 species in the Upper Cretaceous they, and closely related forms, form a continuous 

 varying complex. One can treat such a complex in one of two ways. All described 

 forms can be grouped under one species heading and varieties created or the group 

 may be further subdivided, each new species being clearly defined. Detailed study 

 of the Cenomanian and London Clay forms included within this complex rules out 

 the adoption of the second alternative, since variation is so great as to render the 

 interpretation of separate species, that would be of practical value, difficult if not 

 impossible. 



One of the specimens designated as Xanthidium ramosum by Ehrenberg (1838, 

 pi. 1, fig. 15) was located by Lejeune (1937). This specimen (refigured in pi. 1, 

 fig. 1) and another of Ehrenberg's preparations have been fully studied by one of the 



