. Bulletins of American paleontology. 22 Bulletin 314 20 %f 10 o. o 20 40 60 80 complex axial structure comparative scale 100 open axial region Text-figure 12.—Percent frequency (%f) of values on the axial region comparative scale (see PI. 7, figs. 1-21) for specimens of Grewingkia canadensis (Billings. 1862) from the Richmond Group and three intervals within it, Cincinnati Arch region, n = number of specimens. developed, to those having a simple axial structure with only a few septal lobes, to those in which major septa are withdrawn from the axis leaving an open axial region that lacks septa
. Bulletins of American paleontology. 22 Bulletin 314 20 %f 10 o. o 20 40 60 80 complex axial structure comparative scale 100 open axial region Text-figure 12.—Percent frequency (%f) of values on the axial region comparative scale (see PI. 7, figs. 1-21) for specimens of Grewingkia canadensis (Billings. 1862) from the Richmond Group and three intervals within it, Cincinnati Arch region, n = number of specimens. developed, to those having a simple axial structure with only a few septal lobes, to those in which major septa are withdrawn from the axis leaving an open axial region that lacks septal elements. To compare axial regions within this species, a scale was prepared using 21 specimens arbitrarily assigned values of 0, 5 ... 100 on the basis of decreasing axial region com- plexity as determined by visual comparison (PI. 7, figs. 1-21). Other corals were assigned values by visual comparison with this scale. The frequency distribution of values on the axial region comparative scale for G. canadensis from the entire Richmond Group in the Cincinnati Arch region has a peak at 35, indicating that most individuals have a moderately complex axial structure (Text-fig. 12). Although relatively few values are available for the "Waynesville", the frequency distribution has a peak at 35 with fairly low frequency below 25 and very low frequency above 45. The dis- tribution for specimens from the "Liberty"" has a pro- nounced peak at 35, and frequency below 25 and above 45 is low. For the "Whitewater-Elkhorn"", the greatest peak is at 65. There was apparently a trend in G. canadensis toward predominantly simpler axial regions, although the total range of variability re- mained approximately constant during the Rich- mondian. This trend, like the increase in number of septa, may have been related to decreasing water depth. Too few data are available to determine if fre- quency distributions of values on the axial region com- parative sca
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