PLATE IX. 



Fig. i. Part of a vertical section of Stenopora ovata t Lonsd., from the Carbon- 

 iferous rocks of Queensland, enlarged about twenty-five times, showing the 

 periodical annular thickenings of the corallites, the remote tabulae, placed 

 at corresponding levels in contiguous tubes, and the mural pores. 



Fig. i a. Part of a tangential section of the same specimen, taken just below 

 the surface, and similarly enlarged, showing the hexagonal form of the 

 tubes and the peculiar appearances which they present when the section 

 cuts them across their unthickened or thickened portions. 



Fig. 2. Part of a tangential section of Lyopora favosa, M'Coy, sp., from the 

 Lower Silurian of Craighead, Girvan, enlarged eight times, showing the 

 rudimentary septa, and the thickened walls, in which a few small vacuities 

 are visible. 



Fig. 2 a. Part of a vertical section of another specimen of the same, similarly 

 enlarged, showing the thick walls and the remote complete tabulae. As 

 in the preceding section, a few minute irregular vacuities are seen here 

 and there in- the substance of the wall. 



Fig. 3. A specimen of Nyctopora JSillingsii, Nich., from the Trenton Limestone 

 of Canada, of the natural size ; viewed from above. 



Fig. 3 a. Part of a transverse section of the same, enlarged eight times, show- 

 ing the complete fusion of the walls of the corallites, and the marginal 

 septa, together with an occasional mural pore. 



Fig. 3 b. Part of a vertical section of the same, enlarged eight times, showing 

 the tabulae and mural pores. Where the section cuts through the centre of 

 the tubes, the tabulae are alone seen; where the section passes nearly along 

 the plane of the wall of a tube, the marginal septa and mural pores are 

 brought into view. 



Fig. 3 c. Small part of the surface of the same, enlarged ten times, showing the 

 calices. 



Fig. 4. A small specimen of Billingsia alvcolaris, De Koninck, from the De- 

 vonian of New South Wales, of the natural size (after De Koninck). The 

 corallum is split, and shows the large mural pores connecting contiguous 

 tubes. 



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