PLATE I. 



Fig. I. Fragment of the corallum of Monticulipora {^Heterotrypa) moniliformis, 

 Nich., from the Hamilton Formation (Devonian) of Arkona, Ontario, of the 

 natural size. The specimen shows more conspicuous " monticules " than 

 is usually the case in this species. 



Fig. I a. Portion of the surface of the same, enlarged eighteen times, showing 

 the blunt tubercles or spines (spiniform corallites) between the calices. 



Fig. I b. Portion of a tangential section of the same, enlarged eighteen times, 

 showing the normal corallites, with an occasional small corallite at their 

 angles of junction, and the numerous thick walled hollow spines (spiniform 

 corallites). 



Fig. I c. Part of a vertical section of the same, enlarged eighteen times, show- 

 ing the numerous tabulae, and the thickening of the walls of the corallites 

 as they approach the surface. 



Fig. 2. Fragment of the corallum of Monticulipora (^Heterotrypd) Barraiidi, 

 Nich., from the Hamilton Group (Devonian) of Arkona, Ontario, of the 

 natural size. 



Fig. 2 a. Portion of the surface of the same, enlarged eighteen times. 



Fig. 2 /'. Tangential section of the same, enlarged eighteen times, showing the 

 thick-walled corallites and the occasional development of spiniform tubes. 



Fig. 2 c. Part of the same section, enlarged fifty times. 



Fig. 2 d. Vertical section of the same, enlarged eighteen times. 



Fig. 3. A specimen of Monticulipora {Monotrypa) calceola, Miller and Dyer, from 

 the Cincinnati group of Ohio, of the natural size. 



Fig. 3 a. A smaller example of the same, of the natural size. 



Fig. 3 b. Part of the surface of the same, enlarged eighteen times. 



Fig. 3 c. Tangential section of the same, enlarged eighteen times. 



Fig. 3 d. Part of the preceding section, enlarged fifty times, showing the 

 peculiar small tubes at the angles of junction of the corallites. 



Fig. 3 e. Vertical section of the same, embracing the entire thickness of the 

 corallum, enlarged eighteen times. 



Fig. 4. A fragment of Monticulipora {Heterotrypa) Jtodulosa, Nich., of the 

 natural size, from the Cincinnati group of Ohio. 



Fig. 4 a. Part of the surface of the same, enlarged eighteen times. 



Fig. 4 b. Tangential section of the same, enlarged eighteen times. 



Fig. 4 c. Part of a transverse section of the same, including the narrow peri- 

 pheral zone, and the greater part of the axis, enlarged eighteen times. 



Fig. 4 d. Part of a vertical section, enlarged eighteen times. 



