. Bulletin of the British Museum (Natural History), Geology. 82 SMITH, PAUL, GALE & DONOVAN. Fig. 27 Camera lucida drawings of ambital interambulacral plates (left) and ambulacral plates (right) in Glyphocyphus radiatus () from the Lower Cenomanian of Wilmington. two plates in every three (Fig. 27). In each ambulacral column there are 20 ambulacral pores and 6 primary tubercles at 6-2 mm test diameter, rising to 39 ambulacral pores and 13 primary tubercles at 13-3 mm test diameter (Fig. 25). Primary tubercles are relatively small and decrease in size gradually towards the apex. Mili
. Bulletin of the British Museum (Natural History), Geology. 82 SMITH, PAUL, GALE & DONOVAN. Fig. 27 Camera lucida drawings of ambital interambulacral plates (left) and ambulacral plates (right) in Glyphocyphus radiatus () from the Lower Cenomanian of Wilmington. two plates in every three (Fig. 27). In each ambulacral column there are 20 ambulacral pores and 6 primary tubercles at 6-2 mm test diameter, rising to 39 ambulacral pores and 13 primary tubercles at 13-3 mm test diameter (Fig. 25). Primary tubercles are relatively small and decrease in size gradually towards the apex. Miliary tubercles are abundant and each primary tubercle is separated from those above and below by a single irregular row of miliary tubercles on the single, unbound plate in each triad. Perradially there is a broad zone of dense miliary tubercles, two or three abreast. Small sutural depressions are present and are best developed immediately adoral to each primary tubercle but are also found where three sutures meet (Fig. 27). INTERAMBULACRA. Interambulacral zones are a little less than twice as broad as ambu- lacral zones at the ambitus and in breadth are 34-38% of the test diameter (mean = 36%; SD = 10; N = 25). They are proportionally broader in larger individuals. At 6-2 mm test diameter there are nine interambulacral plates per column but this increases to 14 per column by 13-3 mm test diameter (Fig. 25). Plates at the ambitus are much broader than tall, so that plate height is on average only about 50% of the plate width. Each carries a single small and fairly inconspicuous primary tubercle; it lies slightly off-centre, being a little closer to the adradial suture than to the interradial suture. The tubercle has a relatively large mamelon with a tiny central perforation and a trace of feeble crenulation. The boss is small and the areole forms only 25-30% of the plate width. At the ambitus and adorally the primary tubercles are generally confluent, but above the ambitus a sin
Size: 2725px × 917px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorbritishmuseumnaturalhistory, bookcentury1900, bookcoll
