13^ MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



IGonyaulacysta nannotrix (Deflandre 1939). Upper Jurassic (Kimmeridgian) ; 

 France. 



IGonyaulacysta nealei (Sarjeant 1962ft). Upper Jurassic (Oxfordian) ; England. 



tGonyaulacysta nuciformis (Deflandre 1938). Upper Jurassic (Oxfordian) ; 

 France. 



IGonyaulacysta porosa (Lejeune-Carpentier 1946). Upper Cretaceous ; Belgium. 



?Gonyaulacysta transparens (Sarjeant 1959). Middle Jurassic (Callovian) ; 

 England. 



Genus ACANTHOGONYA ULAX nov. 



Derivation of name. Greek, akantha, thorn, prickle ; a spiny variant of the 

 Gonyaulax tabulation type. 



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

 polyhedral, with the tabulation 3-4', o-ia, 6", 6g, 6'", ip, 0-1 p. v., 1"". Cingulum 

 strongly or weakly helicoid ; sulcus generally or constantly extending on to epitract. 

 Apical horn present only infrequently ; median and antapical horns lacking. 

 Sutures in form of low ridges bearing rows of spines, simple or furcate, or distinguish- 

 able only as rows of spines. Shell bearing general cover of simple or furcate spines, 

 identical to or differing from those on sutures ; spines fewer or totally lacking on 

 cingulum and/or sulcus. Length of spines always less than \ of shell width. Surface 

 smooth, granular, nodose, punctate or reticulate. Precingular archaeopyle formed 

 by loss of plate 3". 



Type species. Gonyaulax venusta Klement i960. Upper Jurassic (Oxfordian to 

 Kimmeridgian) ; Germany. 



Remarks. There are a group of Upper Jurassic species characterized by posses- 

 sion of a dense spine cover, through which a tabulation of Gonyaulax type may be 

 determined with varying degrees of difficulty. It is probable that these forms 

 developed into spinous species without tabulation. These species form a coherent 

 group which are considered to merit a separate generic name. Gonyaulax venusta is 

 selected as type-species, since it shows the tabulation most clearly. 



Forms of Gonyaulacysta with a coarsely tubercular surface, such as G. aculeata 

 (Klement i960) may represent a transitional stage to Acanthogonyaulax. 



The following species accord with the diagnosis of this genus : 



Acanthogonyaulax acanthosphaera (Sarjeant 1961) comb, nov., Upper Jurassic 

 (Oxfordian) ; England. 



A . paliuros (Sarjeant 1962a) comb. nov. Upper Jurassic (Oxfordian) ; England. 



