MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 199 



X. FURTHER DINOFLAGELLATE CYSTS FROM THE SPEETON CLAY 



By W. A. S. SARJEANT 



INTRODUCTION 



The assemblages of dinoflagellate cysts from the Speeton Clay are both extremely 

 rich and extremely varied. Their description was begun in a previously published 

 paper (Neale & Sarjeant 1962) and a number of species are here dealt with, wherever 

 appropriate, in earlier chapters. All remaining species represented that have been 

 studied to date are described in this chapter, and the stratigraphical distribution of 

 all the constituent species of the assemblages is summarized in tabular form and 

 discussed. 



Genus NETR ELYTRON Sarjeant 1961a : 113 



Emended diagnosis. Cavate dinoflagellate cysts, enclosing body spindle-shaped, 

 inner body ovoidal to spindle-shaped. Shell showing no trace of tabulation or of 

 cingulum or sulcus. Shell enclosed in cloak of adherent organic matter, formless or 

 oval to spindle-shaped in outline : fragments of mineral matter and other sediment- 

 ary debris sometimes embedded in cloak. Archaeopyle frequently developed : 

 precingular in position. 



Type species. Netrelytron stegastum Sarjeant 1961a. Upper Jurassic (Oxford- 

 ian) ; England. 



Remarks. This genus is characterized by its shape, cavate character and invest- 

 ing mass of organic matter ; formation of a similar debris cloak during encystment 

 is known to occur in some modern dinoflagellates. 



The genus Kalyptea Cookson & Eisenack 19606 from the Upper Jurassic of Austra- 

 lia, is described as having a " diaphanous veil-like external membrane ", which may 

 correspond to the organic cloak of Netrelytron ; the cysts are oval, with one to two 

 horns, but lack an inner body. The somewhat similar genus Koniewuia Cookson & 

 Eisenack 1960&, also from the Upper Jurassic of Australia, lacks either outer cloak or 

 inner body. 



Netrelytron trinetron sp. nov. 

 PL 22, fig. 3 ; Text-fig. 51 



Derivation of name. Greek, tri-, three ; netron, spindle : referring to the 

 similar shapes of the debris cloak and the enclosing and inner bodies. 



Diagnosis. A Netrelytron with outer body of basically ovoidal shape, giving rise 

 to strongly tapering, conical apical horn and somewhat shorter, conical antapical 

 horn. Shape of inner body exactly similar. Horns polar and axial in position and 

 direction. Endophragm and periphragm minutely, but densely, granular. 



