MESOZOIC AND CAINOZOIC DINOFLAGELLATE CYSTS 43 



proximal crests. Surface of central body slightly granular or rarely reticulate. 

 Processes only gonal, simple or branched, and always open distally. Reflected 

 tabulation is 3-4', 6", 6c, 5'", 1"". 



Holotype. B.M.(N.H.), slide ¥.51989(1). 106 feet above base of London Clay ; 

 Whitecliff Bay, Isle of Wight. 



Dimensions. Holotype : diameter of central body 58 by 62[i, length of processes 

 up to 32(jl. Range : diameter of central body 54-68^, length of processes 24~36[x. 

 Number of specimens measured, 4. 



Description. The endophragm of the central body is i - 5-2[x thick and the 

 periphragm up to i[x. The processes terminate distally in three or more secae, 

 which may be patulate, flaring or recurved. The tips of the secae may be oblate, 

 bifid or bifurcate. This species occurs throughout the London Clay of England. 



Remarks. H. buccina sp. nov. is distinguished from all other species of Hystri- 

 chosphaera, except H. tertiaria (Eisenack & Gocht), by the characteristic form of the 

 processes. H. buccina differs from H. tertiaria in the tabulation, the latter reflecting 

 5 precingular and 5 postcingular plates, 4 elongate rhombohedral cingular plates and 

 a fifth triangular cingular plate. In H. buccina 6" is reflected and is triangular, 

 whilst 6c runs along its antapical edge. Often the boundary between 6" and 6c is 

 ill-defined and may only be seen at high magnification. H. tertiaria has only three 

 apical plates whereas H. buccina may have 3 or 4. When 4 are present 1' and 4' are 

 both narrow elongate plates and are in fine with the corresponding shortened sulcus. 

 The processes of one of the London Clay specimens are reticulate or occasionally 

 perforate, but their form is different from that of H. perforata sp. nov. 



Hystrichosphaera cornuta Gerlach 

 PI. 4, fig. 7 ; Text-fig. 12 



1 961. Hystrichosphaera cornuta Gerlach : 180, pi. 27, figs. 10-12. 



Description. The specimens are identical to those described by Gerlach (1961) 

 and possess the following reflected tabulation — 3-4', 6", 6c, 5'", ip, 1"", with plate 

 6" triangular in outline. Whilst some species reflect only 3 apical plates, others 

 show an elongate division of plate 1' to give rise to two plates which are in line with 

 the sulcus. There is occasionally an apical bulge which interrupts the otherwise 

 regular outline of the central body and lies immediately below the apical process. 

 Gonal and sutural processes are present, and may occasionally be open. In some 

 individuals the large apical process possesses small lateral spines. 



H. cornuta has only previously been recorded from the Middle Oligocene-Middle 

 Miocene of N.W. Germany by Gerlach (1961). 



Material (figured). B.M.(N.H.) slide ¥.51741(2). 85 feet above base of 

 London Clay ; Sheppey, Kent. 



