PLATE IV. 



Fig. I. Portion of the corallum oi Favositcs clousus, Rom., from the Hamilton 



formation (Devonian) of Arkona, Ontario, of the natural size. In the upper 



portion of the specimen the calices are open. 

 Fig. \ a. K few of the calices of the same, closed with an operculum, enlarged 



five times. 

 Fig. I b. Tangential section of the same, enlarged five times. 

 Fig. I c. Vertical section of the same, enlarged five times. 

 Fig. 2. Pachypora lamdllcornis, Lindst., from the Upper Silurian of Gotland, of 



the natural size. 

 Fig. 2 a. Portion of a tangential section of the same, showing the dense 



secondary deposit of sclerenchyma in the interior of the tubes, enlarged 



seven times, with a single corallite enlarged still further, to show the 



rudimentary septa. 

 Fig. 2 b. Portion of a longitudinal section of the same, similarly enlarged, 



showing the thick walls, remote tabulee, and mural pores. 

 Fig. 2 c. Portion of the surface of the same, enlarged five times. 

 Fig. 3. Portion of the corallum oi Pacliypora {Favosites) cervicortiis, De Blainv., 



from the Devonian of Gerolstein in the Eifel, of the natural size. The 



calices are omitted over the greater portion of the surface. 

 Fig. 3 a. Portion of the surface of the same, enlarged about six times. 

 Fig. 3 b. Portion of a tangential section of a specimen of the same, in which 



the cavities of the fossil are filled with oxide of iron, enlarged seven times. 



The thickening of the walls of the corallites is shown, as well as the lateral 



communication of the visceral chambers of some of the corallites. 

 Fig. 3 c. Portion of a transverse section of the same, taken in the axis of a 



branch, similarly enlarged, showing how greatly the tubes are narrowed by 



secondary deposits of sclerenchyma, the original walls still remaining 



quite distinct. 

 Fig. 3 d. Portion of a longitudinal section of the same, enlarged seven times, 



showing the great and irregular thickening of the corallites near their 



mouths, together with remote tabular, and large-sized mural pores. The 



specimen is partially infiltrated with oxide of iron. 

 Fig. 4. Small and imperfect specimen of Pachypora (Favosites) cristata, E. and 



H., from the Wenlock limestone of Dormington, near Stoke-Edith, of the 



natural size. 

 Fig. 4 a. Portion of the surface of the same, enlarged five times. 

 Fig. 4 b. Portion of the surface of a specimen of Pachypora {Faiiosites) cristata, 



var. major, E. and H., from the same locality, similarly enlarged. 



