PLATE VI. 



Fig. T. A colony of Vermipora clausa, Lindst, from the Upper Silurian of 

 Gotland, enlarged twice. 



Fig. i a. Transverse section of the same, enlarged seven times, showing spini- 

 form septa. 



Fig. i b. Vertical section of the same, enlarged seven times, showing tabula? 

 and mural pores. 



Fig. 2. Portion of the surface of the corallum of Alveolites suborbicularis, Lam., 

 from the Eifel, enlarged seven times, showing no apparent traces of the 

 single septal ridge. 



Fig. 2 a. Portion of a tangential section of the same, also from the Eifel, show- 

 ing the form of the corallites. A few of the tubes show a single septal 

 tooth. Enlarged twelve times. 



Fig. 2 b. Vertical section of the same, enlarged twelve times, showing tabulae. 

 The section cuts the tubes at right angles to their long diameters. 



Fig. 3. Tangential section of Alveolites Labechei, E. and H., from the Upper 

 Silurian of Benthall Edge, enlarged twelve times, showing the compressed 

 tubes and well-developed spiniform septa. 



Fig. 3 a. Vertical section of the same, enlarged twelve times, showing the 

 spiniform septa, and the tabulag. The section cuts the corallites parallel 

 with their short diameters. 



Fig. 4. Portion of a tangential section of Alveolites Goldfusst, Bill., from the 

 Hamilton Group (Devonian) of Canada, enlarged twelve times, showing 

 the thin-walled compressed tubes, and the absence of septal spines or 

 ridges. 



Fig. 5. A fragment of Cxnites juniperimis, Eichw., of the natural size, and en- 

 larged five times. From the Wenlock Limestone of Stoke-Edith. 



Fig. 5 a. Part of a vertical section of the same, enlarged twelve times, show- 

 ing the thickening of the tubes close to the mouths, the tabulae, and the 

 mural pores. 



Fig. 5 b. Portion of a transverse section of a branch of the same, enlarged 

 twelve times, showing the compressed corallites in the axis of the stem, 

 with unthickened walls. 



