MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 141 



Remarks. The generic diagnosis is emended to include reference to mode of 

 archaeopyle formation and to specify the correspondence of spine position to sutures. 

 This revision follows the examination of specimens of the type species preserved in 

 flint (see below). The genus as now redefined differs from Gonyaulacysta in the height 

 of sutural spines ; from Xiphophoridium in mode of archaeopyle formation ; and 

 from Heliodinium in the rounded, not flattened, nature of the spines and the less 

 well-marked sutures. 



Hystrichodinium pulchrum Deflandre 



PL 16, figs. 7, 8 



1935. Hystrichodinium pulchrum Deflandre : 229, pi. 5, fig. 1 ; text-figs. 9-1 1. 

 1936a. Hystrichodinium pulchrum Deflandre ; Deflandre : 58, text-fig. 101. 

 1936b. Hystrichodinium pulchrum Deflandre ; Deflandre : 34, pi. 8, figs. 3-8, pi. 9, fig. 3. 

 1 941. Dinoflagellate W. Wetzel, O. Wetzel & Deflandre, text-fig. 7. 



1944. Hystrichodinium pulchrum Deflandre 

 1952a. Hystrichodinium pulchrum Deflandre 

 19526. Hystrichodinium pulchrum Deflandre 

 1955. Hystrichodinium pulchrum Deflandre 

 1959. Hystrichodinium pulchrum Deflandre 

 1961. Hystrichodinium pulchrum Deflandre 

 1963. Hystrichodinium pulchrum Deflandre 



de Wit, unnumbered text-fig. 



Deflandre, text-fig. 103. 



Deflandre, text-fig. 300B. 



Valensi : 591, pi. 3, fig. 11. 



Gocht : 58, pi. 3, figs. 11a, b, pi. 5. fig. 7. 



Alberti : 14, pi. 8, figs. 6-10. 



Gorka : 32, pi. 5, fig. 5. 



Material (Figured). B.M.(N.H.) slide V.13937 (1, 2). Flint from the Chalk 

 (no locality or horizon). 



Dimensions. Figured specimens : No. 1 : overall length I02[i, breadth 98^, 

 shell length 55^, breadth 44^. No. 2 : overall length ii5(x, breadth 8o;i. ; shell 

 length 55fi, breadth 35^. Observed range ; overall lengths i02-H5(x, breadths 

 8o-ioi(a. 



Remarks. This species has long been known from the Upper Cretaceous flints, 

 although its structure has not yet been fully determined. It appears to be synony- 

 mous with the species described by White (1842 : pi. 4 div. 3 fig. 6 ; 1844, pi. 8, 

 fig. 5) and by Wilkinson (1846, pi. 8, figs. 2-3) as Xanthidium spinosum ; this species 

 was subsequently transferred to Hystrichosphaeridium by Deflandre (1937a : 31) and 

 to Baltisphaeridium by Downie & Sarjeant (1963 : 92) on taxonomic grounds, but 

 has never been redescribed. Prolonged enquiry by the present author among the 

 universities, libraries and museums of Britain indicates that the holotypes of White 

 and Wilkinson are lost ; since Hystrichodinium pulchrum is well-defined and a name 

 in widespread use, it is proposed that the earlier name spinosum be abandoned. 



The above enquiry brought to light a number of unlocalized flint slides, in each 

 case of unspecified source, which contain specimens of " xanthidia ", including a 

 number of examples of Hystrichodinium pulchrum. Examination of these indicated 

 the precingular character of the pylome and that the distribution of spines corres- 

 ponds to the positions of sutures, necessitating revision of the generic diagnosis. A 

 full restudy and redescription of this species, based on material extracted by chemical 

 techniques, is clearly necessary. 



