. Bulletin of the British Museum (Natural History), Geology. LATE CAMPANIAN-MAASTRICHTIAN ECHINOIDS 175 there are a few specimens ( EE3581) in which the pore-pairs are in uniserial arcs right to the apex. Each plate carries a single large primary tubercle that occupies most of the plate (PI. 15, fig. 7; Figs 38A, B). This has a relatively well-developed imperforate mamelon and is distinctly crenu- late, though the surrounding platform is not very broad. Areoles are circular and separated by a single ring of small secondary and miliary tubercles. There are 53 pore-pairs in a column at 11 mm
. Bulletin of the British Museum (Natural History), Geology. LATE CAMPANIAN-MAASTRICHTIAN ECHINOIDS 175 there are a few specimens ( EE3581) in which the pore-pairs are in uniserial arcs right to the apex. Each plate carries a single large primary tubercle that occupies most of the plate (PI. 15, fig. 7; Figs 38A, B). This has a relatively well-developed imperforate mamelon and is distinctly crenu- late, though the surrounding platform is not very broad. Areoles are circular and separated by a single ring of small secondary and miliary tubercles. There are 53 pore-pairs in a column at 11 mm test diameter, rising to about 100 pore-pairs at 34 mm test diameter (Fig. 38). Tubercles are largest at the ambitus and decrease in size gradually both adapically and adorally. Adorally there are very strong phyllodes composed of circular pore-pairs with well-developed periporal muscle attachment areas (PI. 15, fig. 10). These phyllodes are so large as to make up more than half of the ambulacral width. Interambulacra are relatively narrow, being only 30-37% of the test diameter in width at the ambitus. There are 10 plates in a column at 11 mm test diameter, rising to 16 at 34 mm test diameter. Each plate carries a large primary tubercle which is imperforate and weakly crenulate. In smaller speci- mens ( less than 35 mm) these are the only large tubercles present, although a distinct small secondary tubercle is present both adradially and interradially. In specimens around 58 mm test diameter the adradial secondary tubercle reaches approximately half the diameter of the primary tubercle at the ambitus and adorally, and there are additional smaller secondary tubercles close to the adradial suture. Primary and secondary tubercles extend to the apex and peristome. The primary tubercles are non-confluent, being separated by a single row of miliaries. The peristome is 30-55% of the test diameter in width (proportionally smaller in larger individuals) and is hardly invaginated,
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