PLATE X. 



Fig. I. Part of a transverse section of Colmnnaria alveolata, Goldf. ( = FavisteUa 

 stellala, Hall), enlarged five times, showing the characters of the septa. 

 From the Cincinnati Group of Ohio. 



Fig. I a. 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 Colmnnaria calkina, 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 tabute, and part of the cut edges of the septa. 



Fig. 3. Part of a transverse section of Colmnnaria (?) Halli, Nich. ( = Colmn- 

 naria 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 

 tabute. In part of the section the cut edges of the septa are seen. 



Fig. 4. Part of a vertical section of Syringopora geniciilata, 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 twenty- 

 five 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 Svringopora reticulata, Goldf, 

 from the Carboniferous Limestone of Kendal, Westmorland, enlarged about 

 fifteen times, showing the spiniform septa, and the cut edges of the tabute. 



Fig. 6. Transverse section of a few of the tubes of Halysitcs cscharoides. Lam., 

 from the Upper Silurian of Gotland, enlarged ten times, showing the spini- 

 form septa, and the apparent absence of any small zooids. 



Fig. 7. Transverse section of a few of the tubes of Ilalysites cateJiularia, Linn., 

 from the Wenlock Limestone of Dudley, enlarged five times, showing the 

 presence of small zooids and the absence of septa. 



Fig. 7 a. Vertical section of another specimen of the same, enlarged five times, 

 showing the tabula; of the larger and smaller zooids. 



