PLATE X.

Fig. 1. Part of a transverse section of Columnaria alveolata, Goldf. ( = Favistella stellata, Hall), enlarged five times, showing the characters of the septa. From the Cincinnati Group of Ohio.

Fig. 1a. Longitudinal section of a single tube of the same, similarly enlarged. Owing to the curvature of the tube, the cut edges of the septa appear in parts of the section.

Fig. 2. Part of a transverse section of Columnaria calicina, Nich., from the Hudson River Group of Canada, enlarged five times, showing the structure of the wall and the characters of the septa.

Fig. 2 a. A single tube of the same, in longitudinal section, similarly enlarged, showing tabulæ, and part of the cut edges of the septa.

Fig. 3. Part of a transverse section of Columnaria (?) Halli, Nich. ( = Columnaria alveolata, of Hall, Billings, &c.), enlarged five times, showing the amalgamation of the walls of the corallites and the marginal septa.

Fig. 3 a. Part of a vertical section of the same, similarly enlarged, showing the tabulæ. In part of the section the cut edges of the septa are seen.

Fig. 4. Part of a vertical section of Syringopora geniculata, Phill., enlarged five times. From the Carboniferous Limestone of Shap, Westmorland. Fig. 4 a. Part of a transverse section of the same specimen, enlarged five times, showing the thickened tubes.

Fig. 4 b. Transverse section of a corallite of the same, enlarged about twentyfive times, showing the contraction of the visceral chamber by a secondary deposit of sclerenchyma within the true wall.

Fig. 5. Transverse section of a single corallite of Syringopora reticulata, Goldf., from the Carboniferous Limestone of Kendal, Westmorland, enlarged about fifteen times, showing the spiniform septa, and the cut edges of the tabulæ. Fig. 6. Transverse section of a few of the tubes of Halysites escharoides, Lam., from the Upper Silurian of Gotland, enlarged ten times, showing the spiniform septa, and the apparent absence of any small zoöids.

Fig. 7. Transverse section of a few of the tubes of Halysites catenularia, Linn., from the Wenlock Limestone of Dudley, enlarged five times, showing the presence of small zoöids and the absence of septa.

Fig. 7 a. Vertical section of another specimen of the same, enlarged five times, showing the tabulæ of the larger and smaller zoöids.