. Bulletin of the British Museum (Natural History), Geology. CRETACEOUS ECHINODERMS FROM WILMINGTON 81 Stratigraphical occurrence and distribution. At Wilmington G. radiatus is not particu- larly common and only 9 stratigraphically located specimens were collected (, ). These specimens come from the lower part of the Grizzle and the upper part of the Wilmington Sand from 231 to 550 cm below standard datum level. G. radiatus is also found in the Lower Cenomanian greensands of Chute Farm, Warminster, from the Cenomanian Grey Chalk of Dover and from the Lower Turonian of Sussex
. Bulletin of the British Museum (Natural History), Geology. CRETACEOUS ECHINODERMS FROM WILMINGTON 81 Stratigraphical occurrence and distribution. At Wilmington G. radiatus is not particu- larly common and only 9 stratigraphically located specimens were collected (, ). These specimens come from the lower part of the Grizzle and the upper part of the Wilmington Sand from 231 to 550 cm below standard datum level. G. radiatus is also found in the Lower Cenomanian greensands of Chute Farm, Warminster, from the Cenomanian Grey Chalk of Dover and from the Lower Turonian of Sussex and south Devon. Description. SHAPE AND SIZE. Tests range in size from 6-2 to 13-3 mm in diameter (mean = 9-5mm; SD = 1-8; N = 25) and from 3-3 to 84mm in height (mean = 5-6mm; SD = IT; N = 24). In profile the test is rather flattened and the ambitus is slightly below mid-height. There is a broad, flat base and a smaller flat apical region. The test height is 53-65% of the diameter (mean = 59%; SD = 3-7; N = 24). In outline the test is circular. Ambulacral and interambulacral tubercles are similar in size and are relatively small and inconspicuous. APICAL DISC. Plates of the apical disc are usually preserved in position and must have been firmly bound to the corona. Ocular plates are all exsert and the apical system is dicyclic (Fig. 26). Each ocular plate is broader than long and no ocular pore is visible from directly above. Genital plates are triangular in outline and have much the same width as ocular plates. A circular gonopore opens at the adambital point of the triangular genital plate. The madre- porite (genital plate 2) is somewhat larger than the other genital plates and is obviously tumid, although it is still relatively small. In outline the apical disc is distinctly oval, with the major axis in the plane passing through ambulacrum III and interambulacrum 5. The major axis of the apical disc is 34-42% of the test diameter (mean = 38%; SD = 21; N = 22) and the width
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