i 7 2 MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 



Diagnosis. A Prolixosphaeridium having an elongate ovoidal central body 

 bearing 60-65 processes. Processes simple or briefly bifurcate (bifurcations unequal- 

 ly long), closed proximally, dominantly or constantly closed distally. Two processes 

 occupying antapical pole ; remaining processes showing alignment in rows, encircling 

 test and offset at a position corresponding to sulcus. Apex typically lost in archaeo- 

 pyle formation ; about six rows of processes present between archaeopyle and 

 antapex, gap between third and fourth row probably corresponding to cingulum. 

 Test surface granular and bearing dense cover of very short spinelets. 



Holotype. B.M.(N.H.) slide ¥".51727(2), Speeton Clay, Shell West Heslerton 

 boring, Yorkshire, Lower Cretaceous (Middle Barremian). 



Dimensions. Holotype : overall length (apex lacking) 62jj. ; overall breadth 

 46fi. ; shell length (apex lacking) ^o\i ; breadth 28[x ; spines c.io-i2[i. long, spinelets 

 i-i-5[x long. Dimensions of other specimens closely similar. 



Description. The distribution of the processes on the epitheca is into three 

 rows ; these appear to respectively comprise 9, 10 and 10 processes. Distribution of 

 processes on the hypotheca was less easily determined. Two rows of processes were 

 present posterior to the presumed cingulum, each apparently comprising 9 processes ; 

 and some 9 further processes clustered round the antapex, probably but not certainly 

 representing a sixth process row. 



The short spinelets form a stubble on the granular surface of the periphragm. 



Remarks. This species was encountered only in the 39 foot horizon in the West 

 Heslerton Borehole. It closely resembles the Upper Jurassic species P. mixtispino- 

 sum (Klement 1960), differing in the broader shell shape (length-width ratio of 

 P. mixtispinosutn consistently greater than 2:1, against a length-width ratio in 

 P. deirense consistently markedly less than 2 : 1) ; in the furcate character of some 

 processes ; and in the somewhat shorter spinelets. These distinctions are minor ; 

 there can be no doubt that P. deirense and P. mixtispinosum are closely related. 



Prolixosphaeridium granulosum (Deflandre) 



1937. Hystrichosphaeridium xanthiopyxides var. granulosum Deflandre : 29, pi. 16, fig. 4. 



1955. Hystrichosphaeridium xanthiopyxides var. granulosum Deflandre ; Valensi : 594, pis. 3, 

 fig. 7, pi. 5, fig. 16. 



1957. Hystrichosphaeridium xanthiopyxides var. granulosum Deflandre ; Downie : 426, text- 

 fig. 46. 



i960. Baltisphaeridium xanthiopyxides var. granulosum (Deflandre) Klement : 59, 



1962a Baltisphaeridium granulosum (Deflandre) ; Sarjeant : 264, pi. 2, fig. 14, text-fig. 8c. 



Remarks. This species, which has a known range from Upper Jurassic to 

 Upper Cretaceous, is represented in the London Clay at Whitecliff and Enborne ; 

 it is, however, possible that these specimens are derived. 



It differs from P. deirense in having only approximately 30 processes, organized 

 into rows, with one antapical process. 



