. Bulletin of the British Museum (Natural History), Geology. CRETACEOUS ECHINODERMS FROM WILMINGTON 87. Fig. 30 Camera lucida drawing of one ambulac- rum of Glyptocyphus difficilis () from the Lower Cenomanian of Wilmington. Note the irregularity of tuberculation and the devel- opment of small pits. N = 13). Each plate carries a single primary tubercle which is imperforate and shows only the faintest trace of crenulation. The mamelon has a relatively flat top and is large in proportion to the size of the boss (PI. 12, figs 3, 4). The primary tubercle is surrounded on three sides by a sc
. Bulletin of the British Museum (Natural History), Geology. CRETACEOUS ECHINODERMS FROM WILMINGTON 87. Fig. 30 Camera lucida drawing of one ambulac- rum of Glyptocyphus difficilis () from the Lower Cenomanian of Wilmington. Note the irregularity of tuberculation and the devel- opment of small pits. N = 13). Each plate carries a single primary tubercle which is imperforate and shows only the faintest trace of crenulation. The mamelon has a relatively flat top and is large in proportion to the size of the boss (PI. 12, figs 3, 4). The primary tubercle is surrounded on three sides by a scrobicular circle of 13 or 14 miliary tubercles. Adradially and perradially there may be a small number of additional miliary tubercles. The areole of primary tubercles is usually marked with feeble radiating ridges. Miliary tubercles are absent adoral of the primary tubercle, where instead two elongate sutural pits may be found; these pits are variably developed and are present only ambitally and adapically. Where sutural pitting is well developed, ambital plates give the appearance of overlapping one another. In larger specimens the three or so most adapical plates lack scrobicular tubercles and there is a prominent interradial naked zone. In these adapical plates the primary tubercles lie slightly towards the adradial edge of the plates. Three or four ambulacral pores lie adjacent to ambital interambulacral plates. PERISTOME. The peristome is more or less circular in outline and its diameter is 36-44% of the test diameter (mean = 40%; SD = 2-1; N = 14). Remarks. The name Cyphosoma difficile was first used by Agassiz (18406), where it appeared without accompanying description or figure. It was not validated until six years later when Agassiz (in Agassiz & Desor) provided a brief diagnosis for the species. The first record of this species in Britain was given by McCoy (1848), who unfortunately attributed the specimen to Agassiz' species Diadema rotulare. Forbes (in Morris 1
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