c.s MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Neotype. Slide AJ97, Laboratoire de Micropaleontologie, Ecole Pratique des 

 Hautes Etudes, Paris. (Figured by Deflandre 1935, pi. 7, fig. 10.) Senonian flint 

 from the Paris Basin. 



Dimensions. Holotype (measured from the illustration) : diameter of central 

 body 32 by 25^, maximum overall diameter 75^, length of processes 18-30^, number 

 of processes, 25. 



Description. The periphragm of the central body is smooth or slightly granular 

 and of the processes is smoother or somewhat fibrous. The processes on a specimen 

 do not vary a great deal in their length or width, the sulcal processes not being 

 significantly smaller. Each process has constant width along its length, widening 

 slightly at the base but not distally, where it terminates in a rosette of short spines. 

 An apical archaeopyle is usually present. The reflected tabulation appears to be 4', 

 6", 6c, 5'", ip, 1"" and 3-6S, and so H. recurvatum is provisionally placed in the 

 genus Hystrichosphaeridium. 



H. recurvatum has only been recorded with certainty from the Senonian of Europe. 



Remarks. Sarjeant (1964a), in a paper on nomenclatural problems, pointed out 

 that on the principle of priority the correct name for this species is H. palmatum and 

 not H. recurvatum. White (1842) referred to this species in the text as Xanthidium 

 recurvatum or palmaforme and in the plate caption as X. palmatum. Thus three 

 alternative names were suggested. Bronn (1848) was next to refer to this species, 

 and listed it as X. palmatum. In 1939 a junior homonym to the latter was proposed 

 by Deflandre & Courteville, this later being transferred to the genus Baltisphaeridium 

 (Downie & Sarjeant 1963). 



Lejeune-Carpentier (1940), overlooking the work of Bronn, described this species 

 under the name of H. recurvatum. Subsequent workers have followed Lejeune- 

 Carpentier and used H. recurvatum as the specific name instead of the correct 

 H. palmatum. Downie & Sarjeant (1964) similarly use H. recurvatum. Since the 

 latter is in general use and H. palmatum (White) Bronn has a junior homonym, it is 

 proposed that H. recurvatum should be retained as the designation for this species. 



A thorough search has been made to find the holotype of H. recurvatum from the 

 British Senonian, figured by White (1842), but without success. It has therefore 

 been necessary to propose a neotype for this species. The neotype proposed was 

 first figured by Deflandre (1935, pi. 7, fig. 10) as Hystrichosphaera tubifera and comes 

 from the Senonian of France (Paris Basin). 



Hystrichosphaeridium sheppeyense sp. nov. 

 PI. n, fig. 3 



1955. Hystrichosphaeridium recurvatum (White) ; Deflandre & Cookson : 269, pi. i. fig. 11. 

 1961. Hystrichosphaeridium recurvatum (White) ; Evitt : 391, 395, pi. 4, figs. 3-5 ; pi. 5, 

 fig. 8. 



Derivation of name. Named after the type locality, the Isle of Sheppey, Kent. 



