i 4 ^ MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



OTHER SPECIES 



The following species are here attributed to the genus Hystrichodinium and accord 

 with the revised diagnosis : 



Hystrichodinium compactum Alberti 1961. Lower Cretaceous (Valanginian) ; 



Germany. 

 Hystrichodinium furcatum Alberti 1961. Lower Cretaceous (Hauterivian) ; 



Germany. 



Hystrichodinium oligacanthum Deflandre & Cookson 1955. Lower Cretaceous ; 

 Australia. 



Hystrichodinium ramoides Alberti 1961. Lower Cretaceous (Barremian) ; Ger- 

 many. 



The two remaining species previously attributed to this genus are considered only 

 doubtfully referable to the revised genus. ? Hystrichodinium amphiacanthum 

 Cookson & Eisenack 1958, has appendages which are polar in position and may 

 warrant erection as a new genus. ?//. parvum Alberti 1961, from the Lower Creta- 

 ceous (Aptian) of Germany, remains of uncertain generic allocation and merits a full 

 restudy. 



Genus HELIODINIUM Alberti 1961 : 33 



Emended diagnosis. Proximo-chorate dinoflagellate cysts, spheroidal, ovoidal 

 or subpolygonal in shape, with tabulation ?3', ?oa, 6", ?oc, 6'", Pop, 1"". Sutures 

 faintly marked by ridges or low crests, from which arise flattened, dagger to ribbon- 

 like, very flexible processes ; processes typically simple, bifurcate or multi-furcate. 

 Cingulum strongly or weakly helicoid, bounded by low crests : sulcus less well 

 marked. Shell surface smooth, granular or punctate. Precingular archaeopyle 

 formed by loss of plate 3". 



Type species. Heliodiniumvoigti Alberti 196 1. Lower Cretaceous (Barremian) ; 

 Germany. 



Remarks. The generic diagnosis is emended to incorporate fuller reference to the 

 tabulation and to include reference to the mode of archaeopyle formation. Helio- 

 dinium is distinguished from Hystrichodinium on the character of its processes. 



Heliodinium voigti Alberti 

 PI. 16, fig. 2 ; Text-fig. 36 

 1961. Heliodinium voigti Alberti : 33, pi. 8, figs. 1-5. 



Emended diagnosis. A Heliodinium having a subpolygonal shell, epitract 

 almost conical and hypotract in form of truncated cone. Tabulation ?3', ?oa, 6", 

 ?oc, 6'", Pop, 1"" ; sutures generally marked only by low ridges, but cingulum and 

 antapex bordered by low crests. Processes dagger-like, frequently highly folded, 

 length less than half shell length ; distal ends of processes typically simple, rarely 

 bifurcate or trifurcate. Shell surface smooth or only minutely granular. 



