The 10 µm scale bar applies to figs. 1-6; the 100 µm scale bar applies to figs. 7-11.
Figs. 1-11. Acrosphaera spinosa. Figs. 1, 7: forma arachnoides. both small specimens without bridges. BSS 28B(VIII/1028) and IOW 144(F). Fig. 2: sporadically occuring form with intermediate characteristics between forma arachnoides as illustrated here and forma lappacea: it lacks the tentlike elevations and bridges, but has flanges. BSS 28B(VIII/1037. Figs. 3, 5, 8-11: forma lappacea. BSS 28B(VIII/903 and 923); BSS 30B(F) EF V46; BSS 32B(F); IOW 144(F) and 140(F). Figs. 4, 6: specimens exhibiting morphological gradation between forma lappacea and forma flammabunda: fig. 6 with incipient bridge-building, fig. 4 without bridges but otherwise quite similar, and with one larger pore with a corona of spines. BSS 28B(VIII/892, 1033).