. Bulletin of the British Museum (Natural History), Geology. 150 Jebel Buhays section 1; loose, derived from lowest few metres of the Simsima Formation (50). Jebel Thanais; lowest 2 m of the Simsima Formation (6). Jebel Rawdah, section 1; bed 4 (1). Jebel Rawdah, section 2; beds 9/10 (2); bed 11 (5); bed 13 (1); loose (6). Jebel Rawdah, section 3; bed 2 (2); bed 5 (1). Jebel Rawdah, section 4; bed 4 (1). Description. Tests range in diameter from 10 to 30 mm, with the great majority around 18-24 mm diameter (Fig. 21). The test is circular in outline and depressed in profile, with a rounded ambi
. Bulletin of the British Museum (Natural History), Geology. 150 Jebel Buhays section 1; loose, derived from lowest few metres of the Simsima Formation (50). Jebel Thanais; lowest 2 m of the Simsima Formation (6). Jebel Rawdah, section 1; bed 4 (1). Jebel Rawdah, section 2; beds 9/10 (2); bed 11 (5); bed 13 (1); loose (6). Jebel Rawdah, section 3; bed 2 (2); bed 5 (1). Jebel Rawdah, section 4; bed 4 (1). Description. Tests range in diameter from 10 to 30 mm, with the great majority around 18-24 mm diameter (Fig. 21). The test is circular in outline and depressed in profile, with a rounded ambitus, although some specimens are slightly more conical. Test height is 39-57% of the diameter (mean = 50%, SMITH SD = 4-0%, N = 30; Fig. 21). The ambitus lies at about mid-height. The apical disc is highly sculpted and occupies 25-42% of the disc diameter (mean = 32%, SD = 1-2%, N = 30). It is proportionally larger in small individuals (Fig. 21). The periproct is large and central, occupying 30-50% of the apical disc diameter (mean = 40%, SD = 4-9%, N = 28). It is oval in outline with smoothly rounded edges (PI. 8, figs 1, 2). The apical disc is dicyclic and all five genital plates are approxi- mately equal-sized (Fig. 22B). There is a rim surrounding the periproct which bears a large central tubercle and two lateral tubercles. The gonopores open at the outer edge of the genital plates. The madreporite has a horse-shoe-shaped zone of madrepores that open around its margin (Fig. 22B). 20 £15 E »10 *v tm 25 c E 3 p 20 ⢠15 n Q. E â Ambulacrum (compound) ⦠Interambulacrum 10 20 30 Test diameter (mm) â â â â â â â â ** ⦠⦠â¦ii»i ⦠⦠⦠⦠⦠⦠⢠⢠⢠⦠⦠20 30 Test diameter (mm) 10 E £8 le 10 14 12|- 20 30 Test diameter (mm) E E 10 I 8 I 6 n £ 4 f â o 5 2. 20 30 Test diameter (mm) ⦠Interambulacrum â Ambulacrum »* «â¢â¦ ⦠⦠⦠⦠t ⦠I e I 4 ..!â â"* â Aoical disc ⦠Perip
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