124 C. E. Gordon — Early Stages in Paleozoic Coral*. 



The corallum of Strejytelasma prof and urn in figure 16 is 

 represented as split on the counter septum and rolled out ; the 

 point toward which the heaviest lines converge is the apex ; 

 the curved line is the circumference of the calyx ; (C) is the 

 counter septum ; (S), the secondary septa ; (T), the tertiary 

 septa ; (Card), the cardinal septum. The corallum was so small 

 and fragile that it was impracticable to attempt drawing to an 

 exact scale, as the measurements could not be made in the cor- 

 allum without the risk of breaking it. Care was exercised not 

 to exaggerate the relations of the septa, so that in the drawing, 

 though necessarily more or less diagrammatic, one sees a very 

 close approximation to the actual appearance. In this figure 

 it is obviously impossible to represent anything but lengths. 

 In doing this I have tried to be true to facts. At the base of 

 the corallum (and in describing the corallum from now on it 

 must be remembered that we are looking down into the vase 

 of the corallum) the septa are not so deep (by depth I mean 

 extension from the wall inward) as a little way up, as though 

 they had undergone resorption or ceased to grow. In modern 

 corals a resorption of the mesenteries takes place at the base, 

 as the animal grows upward.* It is not unlikely that this is 

 the explanation of the tapering off that was observable in all 

 the septa which extended deepest into the calyx. Of the four 

 primary septa represented in the drawing, the counter ex- 

 tended farthest down, the cardinal next, and the alar septa next. 

 The bending represented in the alar septum on the right is 

 meant to represent the slight deflection of the inner edge of 

 the septum upward, as though the mesentery has been crowded 

 by the counter septum at the base. Attention is directed 

 to the fact that only four septa appear in the early stage of 

 the corallum. The alar septum on the left is appreciably 

 longer than the secondary septum adjacent to the counter 

 represented in the left hand portion of the figure by S. The lat- 

 ter showed greater depth near the base than the corresponding 

 one on the right, as though it had been resorbed to a less 

 extent, or as though it had grown faster. The second second- 

 ary septum in the left hand counter quadrant exhibits a con- 

 dition of unequal growth. The order of development of the 

 secondary septa is plainly seen to correspond exactly to that 

 in the Zaphrentoid coral in figure 15. With respect to the ter- 

 tiary septa, although examined with the aid of a powerful binoc- 

 ular in artificial light, it was impossible in all cases to tell to 

 what length they extended down into the coral. In the cardi- 

 nal quadrants near the main septum they merged with a ridge 



*" Morphology of Coral Polyps,'' J. E. Daerden, Smithsonian Miscella- 

 neous Collection, Quart. Issue, vol. ii, No. 1, 1904, p. 98. 



