. Bulletin of the British Museum (Natural History), Geology. 174 SMITH 40 r ~30 E E 1)20 10 30 | 18 - 16 o. 14 S; 12 o 10 10 20 10 â Ambulacrum ⦠Interambulacrum. 10 20 30 40 Test diameter (mm) â Peristome ⦠Apical disc 50 60 20 30 Test diameter (mm) 20 30 Test diameter (mm) _i 40 40 10 20 30 40 50 Test diameter (mm) 60 Fig. 38 Biometric data for Phymechinus? perplexus sp. nov. lacral plate. Mamelons very large and crenulation feebly developed. Lower surface flat, peristome small with feeble buccal notches. Phyllodes extremely well-developed. Description. Tests are 11 to 60 mm in diamet
. Bulletin of the British Museum (Natural History), Geology. 174 SMITH 40 r ~30 E E 1)20 10 30 | 18 - 16 o. 14 S; 12 o 10 10 20 10 â Ambulacrum ⦠Interambulacrum. 10 20 30 40 Test diameter (mm) â Peristome ⦠Apical disc 50 60 20 30 Test diameter (mm) 20 30 Test diameter (mm) _i 40 40 10 20 30 40 50 Test diameter (mm) 60 Fig. 38 Biometric data for Phymechinus? perplexus sp. nov. lacral plate. Mamelons very large and crenulation feebly developed. Lower surface flat, peristome small with feeble buccal notches. Phyllodes extremely well-developed. Description. Tests are 11 to 60 mm in diameter and 5-8 to 31-2 mm in height (test height 50-60% of diameter; mean = 54%, SD = 3-2%, N = 9). They are circular in outline and bun-shaped in profile, with a broad base and depressed conical upper surface (PI. 15, fig. 8). The ambitus lies at approximately 30% of test height above the base. The apical disc is small and circular, only 16-28% of the test diameter across (PI. 15, fig. 9). It is proportionally smaller in larger individuals (Fig. 38). No specimen retains any apical disc plating, but to judge from the small size of the opening, plating is almost certain to have been dicyclic or hemicyclic. Ambulacra are only slightly narrower than interambulacra at the ambitus and measure 23-28% of the test diameter in width (mean = 25-5%, SD = 1-8%, N = 9). They are more or less straight, tapering slightly adorally and more signifi- cantly adapically. All plates are polygeminate with seven (rarely six or eight) pore-pairs to an ambital plate. Plate compounding is in the phymosomatid style (Figs 39A, B). Pore-pairs are strongly arced at the ambitus, but tend to become irregularly biserial or pleuriserial adapically and adorally (Figs 38C, D). Close to the apex, pore-pairs once again become uniserially arranged. Adapically, small second- ary tubercles occur scattered within the pore zone. However,. Please note that these images are extracted from scanned page images that may ha
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