MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 71 



Diagnosis. Subspherical chorate cysts possessing a reflected tabulation of 4', 

 6", 5-6'", ip, 1"". Processes tubiform, open distally, intratabular, one process per 

 plate area. Number of processes never more than 18. Archaeopyle apical. 



Type species. Xanthidium tubiferum complex White 1842. Upper Cretaceous ; 

 England. 



Remarks. Cingular processes are absent, there commonly being 6 postcingular 

 processes. The processes are approximately of equal length on an individual but 

 are variable within a species. They are always open and can be cylindrical to 

 infundibular with perforate or entire walls. Endophragm confined to the central 

 body, surrounded by periphragm which alone forms the processes. Processes never 

 in contact with the interior of the central body. 



An alternative formula for the reflected tabulation is : 4', 6", 5'", ip, 1"" and 

 o-is. In the specimens possessing 14 processes, all are of the same size and one 

 would expect if one sulcal process was present that this would be smaller than the 

 other processes. This corresponds to the typical Gonyaw/ax-tabulation in which 

 there are 6 postcingular plates, plate 1'" sometimes being considerably reduced. 

 The original tabulation is tentatively reconstructed in Text-fig. 1. 



Oligosphaeridium complex (White) 

 PL 7, figs. 1, 2 ; PI. 10, fig. 3 ; Text-fig. 14 



Xanthidium tubiferum complex White : 39, pi. 4, div. 3, fig. 11. 



Xanthidium tubiferum complex White ; White : pi. 8, fig. 10 ; text-figs. 



Xanthidium complexum (White) Bronn : 1375. 



Hystrichosphaeridium elegentulum Lejeune-Carpentier : 22, text-figs. 11, 12. 



Hystrichosphaeridium complex (White) Deflandre : 11. 



Hystrichosphaeridium complex (White) ; Firtion : 156, pi. 9, figs. 2, 4, 5 ; text-fig. 



iA-F. 

 Hystrichosphaeridium complex (White) ; Deflandre & Cookson : 270, pi. 1, figs. 9, 10. 

 Hystrichosphaeridium complex (White) ; Valensi : 592, pi. 4, fig. 3. 

 Hystrichosphaeridium complex (White) ; Cookson & Eisenack : 42, pi. 12, fig. 10. 

 Hystrichosphaeridium complex (White) ; Eisenack : 400 pi. 26, 400, figs. 3-5 ; pi. 25, 



fig. 16? 



1842 

 1844 

 1848 

 1940 

 1946 

 1952 



1955 



1955 



?i 9 58 



1958 



1959 

 ?I962 

 ?ig63 



1964 



Hystrichosphaeridium complex (White) 

 Hystrichosphaeridium tubiferum (Ehr.) 

 Hystrichosphaeridium tubiferum (Ehr.) 

 Hystrichosphaeridium complex (White) 



Gocht : 66, pi. 3, figs. 2, 3 ; pi. 7, figs. 5, 6. 

 Pocock : 83, pi. 15. fig. 230. 

 Baltes, pi. 2, figs. 1-3, 5, 6. 

 Cookson & Hughes : 46, pi. 9, fig. 6. 



Emended diagnosis. Central body sub-spherical to ovoidal. Wall composed of 

 thin endophragm and periphragm, the latter giving rise to processes. Processes 

 simple or branched, cylindrical for most of their length, open and expanded distally 

 with aculeate or secate margin. Reflected tabulation inferred 4', 6", 5-6'", ip, 1"". 

 Apical archaeopyle usually present having zig-zag margin. Processes in complete 

 specimen not exceeding 18. 



Neotype. Geol. Surv. Colin, slide PF.3034(i). Lower Chalk, H.M. Geological 

 Survey Borehole, Fetcham Mill, Surrey, at 750 feet depth. Upper Cretaceous 

 (Cenomanian). 



