MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 235 



Thalassiphora delicata sp. nov. 

 PL 26, fig. 8 



Derivation of name. Latin ; delicatus, tender, dainty. 



Diagnosis. A Thalassiphora with ellipsoidal central body possessing a smooth 

 thin wall. Periphragm in form of wing lamella, delicate, often irregularly folded and 

 turned over on its margin. No keel present. Periphragm can be perforate. An 

 archaeopyle may be present. 



Holotype. B.M.(N.LL) slide V. 51756(3). London Clay; Enborne, sample E 11. 



Dimensions. Holotype : diameter of central body 34 by 43^, overall diameter 

 74 by 75fA. Observed range : diameter of central body 34-57EA, overall diameter 

 74-i20(x. Number of specimens measured, 4. 



Description. T. delicata exhibits considerable variation in width of the peri- 

 phragm, this is partly due to unequal folding. Some of the folds on the periphragm 

 suggest the presence of a cingulum ; this is however difficult to visualise since the 

 periphragm does not completely surround the central body. Both the endophragm 

 and periphragm are thin. 



Remarks. This is only the third species allocated to this genus. It differs from 

 the other two in size, the extremely thin periphragm and endophragm, the commonly 

 perforate periphragm and the absence of a keel. 



XII. acknowledgments 



The authors have received help from many specialists in varying degree and would 

 like to express their thanks for the ready and full co-operation afforded them. In 

 particular they would like to thank Prof. Georges Deflandre, for much help and for 

 courtesy in entertaining two of the authors (R.J.D. and W.A.S.S.) and allowing 

 them to examine holotypes at the Laboratoire de Micropaleontologie, Ecole Pratique 

 des Hautes Etudes, Paris ; Prof. A. Eisenack and Herr Hans Gocht, for their courtesy 

 in entertaining two of the authors (CD. and W.A.S.S.) and permitting study of 

 holotypes in the collections of the Geologisches Institut, University of Tubingen ; 

 Dr. W. R. Evitt, of Stanford University, California, for much assistance in the formu- 

 lation of the concepts here expressed ; Dr. J. W. Neale, of the University of Hull, 

 and Dr. P. Kaye, of Burmah Oil Co., for their advice on Speeton Clay stratigraphy ; 

 Mr. D. Curry for his advice on London Clay stratigraphy ; Dr. G. Norris, of McMast- 

 ter University, Hamilton, Ontario, for profitable discussions, particularly on Gony- 

 aulacysta and allied forms ; Dr. K. Diebel, of the Institut fur Palaontologie, 

 Humboldt University, Berlin, for courteously permitting the loan, for study, of 

 Ehrenberg's holotypes ; and Professors W. D. Evans and L. R. Moore, of the 

 Universities of Nottingham and Sheffield, for their help and encouragement. 



They would further like to acknowledge the courtesy of Shell Internationale 

 Research Maatschappij J.V., the Hague, Netherlands, for permitting study of 

 Speeton Clay specimens from the West Heslerton No. 1 Borehole and for permitting 



