. Bulletin of the British Museum (Natural History). . Fig. 145 Tholopora dightonisp. nov., BM(NH) D57672, holotype; MSA, colony surface showing parts of two subcolonies, x 30; 145B, rows of autozooecia separated by kenozooecia, x 85; 145C, mural spines in autozooecia and kenozooecia, x 300; 145D, partly overgrown and broken gynozooecium, x 38; see also Fig. 144. Description. Zoaria are short (Figs 146, 147A), generally less than 1 cm in height, and consist of a series of stacked bun- shaped subcolonies, sometimes bifurcating. Branches are typically 3^ mm in diameter with annular cons
. Bulletin of the British Museum (Natural History). . Fig. 145 Tholopora dightonisp. nov., BM(NH) D57672, holotype; MSA, colony surface showing parts of two subcolonies, x 30; 145B, rows of autozooecia separated by kenozooecia, x 85; 145C, mural spines in autozooecia and kenozooecia, x 300; 145D, partly overgrown and broken gynozooecium, x 38; see also Fig. 144. Description. Zoaria are short (Figs 146, 147A), generally less than 1 cm in height, and consist of a series of stacked bun- shaped subcolonies, sometimes bifurcating. Branches are typically 3^ mm in diameter with annular constrictions between the subcolonies, each of which is about 0-9 mm in height. New subcolonies originate close to the centres of existing subcolonies and zooecial chambers may be con- tinuous between parent and daughter subcolonies when seen in thin section. Autozooecia are variable in size and arranged in irregular ill-dcfincd radiating uniserial rows (Fig. 147B) separated by smaller kenozooecia, also irregularly arranged and variable in size. Within each row successive autozooecia are not always contiguous but may be separated by kenozooecia (cf. T. thornasi and T. dightoni). No mural spines have been observed, but details of fine preservation are obscured by secondary crystals of calcite in available material. The single brood chamber observed (Fig. 148B) is roughly circular in outline, about 1 •6-2-0 mm in diameter, with autozooecia passing through the chamber to support the roof together with internal vertical septa. The ooeciostome is not recognizable. In thin section zooecial walls have a cloudy, granular appearance without obvious laminations. Dark transverse bands may occur which resemble monilae but the walls are parallel-sided. Exozonal wall thickness attains 0-03 mm. Of common occurrence are thin, aborally-flexed diaphragms (probable subterminal diaphragms) located 0-2-0-3 mm proximal of the zooecial aperture. Distinction between auto- zooecia and kenozooecia is not
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