. Bulletin of the British Museum (Natural History), Geology. FROM GREAT BRITAIN AND FRANCE 247 Dimensions. Holotype : overall length 40 p, breadth 40 /x ; length of the spines 3 fi. Figured specimen : overall length 34 /z, breadth 33 ti ; spines length 2-3 p. Description. Theca almost spherical, but having a somewhat polygonal appearance because of the angularly set spine rows on the plate boundaries. Four apical plates are present. Plate 1' is the largest ; the boundary between plates 1' and 4' was not clear. The six precingular plates, together with the apical plates form the epitract ; ther
. Bulletin of the British Museum (Natural History), Geology. FROM GREAT BRITAIN AND FRANCE 247 Dimensions. Holotype : overall length 40 p, breadth 40 /x ; length of the spines 3 fi. Figured specimen : overall length 34 /z, breadth 33 ti ; spines length 2-3 p. Description. Theca almost spherical, but having a somewhat polygonal appearance because of the angularly set spine rows on the plate boundaries. Four apical plates are present. Plate 1' is the largest ; the boundary between plates 1' and 4' was not clear. The six precingular plates, together with the apical plates form the epitract ; there is no anterior intercalary plate. Plate 1" is reduced to accommodate of plate 2'. Plates 2", 3", 4" and 5" are more or less uniform in size and shape, but plate 6" is different in shape because of the broadening sulcus. The cingulum is occupied by six plates of moderate size. The sulcus extends onto. Fig. 4. Cryptarchaeodinium calcaratum (Deflandre). Specimen, showing the tabulation and the precingular archaeopyle (plate 3" is missing). Left, ventral view; right, dorsal view. xc. 1400. the epitract and the hypotract, from apex to antapex ; it is narrow in its middle portion, being broad in its anterior and posterior portions. Seven postcingular plates of variable size and shape are present. Plates 1" ', 6" ' and 7" ' are small, whereas plate 4" ' is largest of all the plates of the shell. Two posterior intercalary plates are located on the two sides of the posterior end of the sulcus. The single antapical plate 1" ' is a rather small plate. Remarks. The diagnosis of C. calcaratum is emended to include the presence of the archaeopyle and the detail of the tabulation. This study was based on a single but excellently preserved specimen from the Kimmeridge Clay of Stretham. Deflandre first observed C. calcaratum in the assemblages from Orbagnoux in 1939 ; a fuller diagnosis was given in 1941 and quoted again in 1952. The
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