i )( MESOZOIC AND CAINOZOIC DINOFL AGELLATE CYSTS 



The shell surface appears devoid of ornamentation. The processes are flattened 

 and very flexible, generally simple — one process in the figured specimen is bifurcate, 

 one trifurcate. 



Plate 3" is generally lost in pylome formation. 



Remarks. The diagnosis of this species is emended to incorporate new observa- 

 tions. Alberti (1961 : 33) noted the presence of an archaeopyle in one specimen, 

 but did not refer to this in the diagnosis. 



The stratigraphic range of the German specimens is Lower Barremian to ? Lower 

 Aptian : the English occurrence thus represents a vertical extension of this range. 



Heliodinium patriciae Neale & Sarjeant 

 PI. 16, fig. 1 



1961. Heliodinium patriciae Neale & Sarjeant : 451, pi. 19, fig. 3 ; text-fig. 7. 



Remarks. Re-examination of the holotype (B.M.(N.H.) slide V.51710), and 

 other specimens, suggests a similar tabulation to that of H. voigti ; the mode of 

 archaeopyle formation was not determined. In the original text fig. 7, the number 

 of processes shown arising from the cingulum margins is now considered to be some- 

 what exaggerated ; the figure is correct in all other particulars. 



B. Genera with apical archaeopyle 



Genus MEIO UROGONYA ULAX nov. 



Derivation of name. Greek, meiouros, curtailed, shortened ; a variant of the 

 Gonyaulax tabulation type shortened by loss of the apex in archaeopyle formation. 



Diagnosis. Proximate dinoflagellate cysts, spherical, ellipsoidal, ovoidal or 

 polyhedral, with the tabulation, 4', o-ia, 6", 6g, 5-6'", o-ip, 0-1 p. v., 1"". Cingu- 

 lum strongly or weakly helicoid ; sulcus generally or constantly extending on to 

 epitract. Sutures in form of low ridges or bearing crests of varied form (smooth, 

 denticulate or spinous ; perforate or imperforate). Height of crests always less than 

 I of shell width. Surface smooth, granular, nodose, punctate or reticulate. Arch- 

 aeopyle formed by loss of apical plates, part of plate 1' sometimes left attached to 

 shell ; not all individuals show an archaeopyle. 



Type species. Meiourogonyaulax valensii sp. nov., Middle Jurassic. 



Remarks. This genus presently contains a small group of Jurassic species ; 

 unpublished data available to the author suggests the probability that a number of 

 additional species will be described in the future from the Lower and Middle Jurassic. 



The apex has in no case been satisfactorily seen in position. The number of apical 

 plates is deduced from the irregular profile of the archaeopyle and may be subject to 

 future correction. 



