154 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



D. Genera with cingular archaeopyle 

 Genus CTENIDODINIUM Deflandre 1938 : 181 



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

 ellipsoidal or polygonal, having the tabulation 3-4', o-ia, 6", 6c, 6'", ip, 0-1 p. v., 

 1"" ; sutures in form of low ridges bearing crests of varied form, typically but not 

 constantly high and denticulate. Cingulum strongly or weakly spiral, laevo- 

 rotatory ; suture on anterior margin of cingulum lacking crest, crest on posterior 

 margin very high. Archaeopyle (where present) formed by schism along cingulum. 



Type species. Lithodinia jurassica var. omata Eisenack 1935. Middle Jurassic 

 (Callovian) ; Germany. 



Remarks. The diagnosis is emended to include reference to tabulation and mode 

 of archaeopyle formation ; the latter, in combination with the unequal crest develop- 

 ment on either side of the cingulum, characterizes the genus. Both species currently 

 attributable to the genus occur in the Middle to Upper Jurassic (Callovian to Oxfordi- 

 an), the type species being known to range up into the Lower Oxfordian. 



other species 

 The following species also accords with the revised diagnosis of the genus : 

 Ctenidodinium tenellum Deflandre 1938. Upper Jurassic (Oxfordian) ; France. 



Genus WANAEA Cookson & Eisenack 1958 : 57 



Type species. Wanaea spectabilis Cookson & Eisenack 1958. Upper Jurassic ; 

 New Guinea. 



Remarks. W. R. Evitt, in litt., has informed the writer that this genus comprises 

 detached epitracts and hypotracts of a genus with a Gonyaulax-pa.ttem tabulation. 

 High crests, perforated in varying degree to give a fringe-like appearance, border the 

 cingulum : crests elsewhere on the shell are marked only by low ridges. Archaeopyle 

 formation apparently results from schism along the cingulum, but the mechanism of 

 the process appears more complicated than in Ctenidodinium. A full study of the 

 genus is understood to be in press. 



E. Genera with archaeopyles formed by other means 



Genus PLURIARVALIUM Sarjeant 1962a : 260 



Type species. Pluriarvalium osmingtonense Sarjeant 1962a. Upper Jurassic 

 (Upper Oxfordian) ; England. 



Pluriarvalium osmingtonense Sarjeant 

 Text-fig. 40 

 1962a. Pluriarvalium osmingtonense Sarjeant : 262, pi. 1, fig. 5 ; text-fig. 6. 



Remarks. This species is relatively abundant in certain horizons of the Upper 

 Jurassic ; all specimens observed to date are either intact or severely damaged and 



