PLATE XIII. 



Fig. i. Part of a tangential section of Monticulipora (Heterotrypa} mammulata, 

 D'Qrb., from the Cincinnati Group of Cincinnati, Ohio, enlarged twenty 

 times, showing the two sets of corallites. 



Fig. i a. Small portion of the preceding section, enlarged fifty times, showing 

 the structure of the walls, and the occasional presence of spines (modified 

 corallites). 



Fig. i b. Part of a vertical section of the same species, enlarged twenty times, 

 showing the different disposition of the tabulae in the two sets of corallites 

 respectively. 



Fig. 2. Part of a tangential section of Monticulipora (Heterotrypa) ramosa, F. 

 and H., from the Cincinnati Group of Cincinnati, Ohio, enlarged twenty 

 times, showing' the two sets of corallites. 



Fig. 2 a. Part of a vertical section of the same species, enlarged twenty times, 

 showing the different disposition of the tabulae in the two sets of tubes. 



Fig. 3. Under surface of a specimen of Monticulipora (Diplotrypa) petropolitana, 

 Pand., from the Lower Silurian rocks of Sweden, of the natural size, show- 

 ing the epithecal plate. 



Fig. 3 a. The same specimen, viewed in profile, of the natural size. 



Fig. 3 b. Part of a tangential section of the same, enlarged twenty times, show- 

 ing the uniformly thin walls of the corallites, and the small angular tubes 

 wedged in at the angles of junction of the larger ones. 



Fig. 3 c. Part of a vertical section of the same, showing the two sets of tubes, 

 and the increase in the number of the tabula? as the exterior is approached, 

 enlarged twenty times. 



Fig. 4. Under surface of Monticulipora (Diplotrypa) Whiteavesii, Nich., of the 

 natural size, showing the concave base and epithecal plate. From the 

 Trenton Limestone of Peterboro', Ontario. 



Fig. 4 a. The same specimen viewed in profile. 



Fig. 4 b. Part of a tangential section of the same, enlarged twenty times, show- 

 ing the different groups of corallites. 



Fig. 5. Side view of a specimen of Monticulipora (Monotrypa) Winteri, Nich., 

 of the natural size, from the Devonian Limestone of Gerolstein in the 

 Eifel. 



Fig. 5 a. Under surface of the same, of the natural size, showing the epithecal 

 plate partially removed by weathering. 



