30 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



thus they are not furcate. His figures are certainly not in accordance with those of 

 Ehrenberg, and probably represent a different species. White's figures of X. 

 ramositm closely resemble those of Ehrenberg for this species and are probably 

 correct. The processes are predominantly trifurcate, often with a small bifurcation 

 at their extremities. 



X. ramositm had been figured earlier, without description, by Reade (1839) but his 

 figure more closely resembles X. complex White than Ehrenberg's figures of X. 

 ramositm. Ehrenberg (1854) refigured some of his specimens but again they were 

 not accompanied by a text description. 



O. Wetzel (1933) erected the genus Hystrichosphaera making both H. furcata and 

 H. ramosa type species, this being contradictory to the rules of nomenclature. H. 

 furcata is described as having strongly built processes with short bifurcations 

 distally, each branch terminating in two spines. In H. ramosa some of the processes 

 are divided into two, rarely more, they branch approximately half way along their 

 length and finally divide into spinelets, usually three in number. The descriptions 

 correspond with Ehrenberg's specimens, but O. Wetzel's plates are not distinct. 

 Both species possess central bodies which are divided into fields or areas by sutures, 

 from the junctions of which 6 to 30 processes arise. An equatorial girdle is often 

 present. O. Wetzel considered H. furcata and H. ramosa to be varieties of the same 

 species, and contrary to the rules of nomenclature, proposed a new name H. com- 

 munis to contain them. 



Deflandre (1935, 1936) figured a specimen of H. furcata which differs from Ehren- 

 berg's types in that there is a proximal membrane and the majority of the processes 

 have trifurcate extremities. Later (1937) he published the first account of the 

 tabulation of H. furcata and also mentioned the well developed apical process. He 

 pointed out that the processes invariably arose from nodal points at the junction of 

 the plates. The processes are short and predominantly trifurcate, although some 

 bifurcate processes do occasionally occur. The number of processes is approxi- 

 mately 30. The processes are not of equal length and tend to be shortest in the 

 region of the triangular plate and longest at the poles. H. ramosa as figured by 

 Deflandre differs from H. furcata only in the presence of processes which divide 

 medially into two branches which themselves terminate distally in three spines. 

 Like Wetzel Deflandre also considered H. furcata and H. ramosa to be varieties of 

 one species, but suggested that the names H. furcata and H. furcata var. ramosa 

 would be more appropriate, the latter being applied to individuals having slender 

 and very divided processes. However the plates show only slight differences 

 between the two types. Both possess bifurcate and trifurcate processes with medial 

 branching and proximal membranes ; and considering the slenderness of the 

 processes there is little or no difference. In fact both forms agree very well with 

 X. ramositm of Ehrenberg. 



Lejeune (1937) re-examined Ehrenberg's preparations and rediscovered one of his 

 figured specimens (pi. 1, fig. 1) of X. ramositm. A detailed description of H. ramosa 

 was given by Lejeune accompanied by some excellent figures. The majority of the 



