BROWN, RUGOSE CORALS 
69 
attachment moves inward until they, in some individuals, become equal in 
size with the primary septa and are radially arranged. There are in the 
Columbia collections individuals which show gradations from the conditions 
shown in figure 4 to six equal and radially disposed septa. 
Figure 5 shows the appearance of a second secondary septum in one 
counter quadrant. Figure 6 shows two secondary septa in each counter 
quadrant. Figure 7 is the same stage from another individual and shows 
that a pair of tertiary septa have already appeared, one on either side of the 
counter septum. Attention is especially called to this very early appearance 
of the first pair of tertiary septa adjacent to 
the counter septum. Figure 8 shows the ap¬ 
pearance of the third secondary septum in one 
counter quadrant and the appearance of a 
tertiary septum in the same quadrant. In 
figure 9 we see a tertiary septum present on 
either side of the counter septum, three secon¬ 
dary septa in either counter quadrant, and one 
secondary septum in each cardinal quadrant. 
In figure 10, two secondary septa have appeared 
in each cardinal quadrant, and in figure 11 
four are present in each counter quadrant. In 
figure 12, there are three in each cardinal 
quadrant and five in each counter quadrant. 
Figure 13 has four secondary septa in each 
cardinal quadrant and six in each counter 
quadrant. Attention is called to the grouping 
of the septa in this and the preceding figures. 
Each successive septum to appear in each 
quadrant respectively is attached by its inner Figs . 12 _i 3 . Stereolasma 
border to the side of the previous septum, rectum. (Enlarged.) 
giving in this stage an arrangement of the 
septa similar to the adult condition in Streptelasma profundum, of the 
progressive series at a very much earlier geological time, and also of the adult 
condition of the genus Hadrophyllum, a retrogressive genus occurring late 
in the geological history of the rugose corals. 1 Figure 14 has the same 
number of secondary septa but they are more fully developed and in addi¬ 
tion three more pairs of tertiary septa have been added in the counter quad¬ 
rants and two pairs have appeared in the cardinal quadrants. In figure 15, 
a seventh pair of secondary septa have appeared in the counter quadrants, 
1 See also J. E. Duerden, Biological Bulletin, Vol. IX, No. 1, pp. 35-36, June, 1905. 
