. Bulletins of American paleontology. 48 Bulletin 347. Text-figure 12.—Transverse sections illustrating astogeny and corallile increase in Propora thebesensis. A, Earliest growth stage of a corallum, showing group of similar thick-wallcd corallites; USNM 485701, Section-interval 23-2 (Lawrence Quarry). B1-B4, Serial sections showing corallite increase in axial part of a corallum having broad tabularium spacing; USNM 459087, Section-interval 23-2 (Lawrence Quarry). Cl- C5, Serial sections showing corallite increase in axial part of a corallum having close tabularium spacing; USNM 459076, Sectio
. Bulletins of American paleontology. 48 Bulletin 347. Text-figure 12.—Transverse sections illustrating astogeny and corallile increase in Propora thebesensis. A, Earliest growth stage of a corallum, showing group of similar thick-wallcd corallites; USNM 485701, Section-interval 23-2 (Lawrence Quarry). B1-B4, Serial sections showing corallite increase in axial part of a corallum having broad tabularium spacing; USNM 459087, Section-interval 23-2 (Lawrence Quarry). Cl- C5, Serial sections showing corallite increase in axial part of a corallum having close tabularium spacing; USNM 459076, Section-interval 16-2 (Clinton Spring) (see also PI. 3, figs. 8-11). Corallile walls and septa are solid, tabulae and dissepiments are stippled; scale bar is shown. For B and C, heights in mm arc above an arbitrary datum within the mature part of each corallum; numbers in italics represent individual corallites; an asterisk indicates the first appearance of a particular corallite. closely spaced, dissepiments appear as flat, horizontal plates (PI. 3, fig. 7, PI, 4, figs. 2, 5, 7); where tabularia are widely spaced, dissepiments become more broadly domed (PI. 1, fig. 2, PI. 2, fig. 4). In some places the outer edges of thickened septal trabeculae appear as small nodes or vertical plates on the upper surfaces of dissepiments (PI. 1, fig. 2). In transverse section, dis- sepiments are thin and sparsely distributed (PI. 1, figs. 1, 5). Where cyclomorphic variation in thickness of elements is pronounced, extreme thickening of septal structures may replace the coenenchyme with a dense trabecular mass between adjacent tabularia (PI. 1, fig. 11). Astogeny and corallite /Vjc/'ea^f. —Descriptions are based principally on two serial-sectioned coralla (USNM 459076, 459087) and six serial-sliced coralla (USNM 459075, 485701, 485711, 485712, 485741, 485753). Other specimens are used for comparison. The earliest growth stages are recognized in three coralla. In each of these, the protocorallite
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