278 W. II. SIIERZER — THE GENUS CHONOPHYLLVM. 



the typical Chonophyllum and in the rugosa in general, although from ad- 

 ditional deposits of calcium carbonate a nearly lamellar septum may at 

 times be formed. 



The septa typically terminate some distance from the center, leaving a 

 broad, flat central area. In certain specimens the sharp septal foldings 

 of the cell-cups may continue to near the center as low ridges upon the 

 tabula?. Four fovew are developed in typical forms, but generally one 

 only is at all distinctly defined. The broad longitudinal bands on the 

 cpitheca mark the positions of the interseptal cavities. 



The following points of structure will then ordinarily serve for the 

 separation of Omphyma from Chonophyllum : 



1. Strong radiciform processes. 



2. Broad, well developed tabula?. 



3. Infolding of the cell-cups to form sharply crested or angular septa. 



4. Absence of supporting processes. 



5. The coarse, subvesicular structure of the interseptal cavities. 



6. The generally broad, smooth central area. 



7. The presence of one or more fovea?. 



8. The broad costal bands representing the interseptal cavities. 



Ptychophyllum, Edwards and Haime, 1850. 



The type of this genus, as given by the founders, is P. stokesi, E. and H., 

 from Drummonds island, lake Huron. Owing to the development of 

 radiciform processes, similar to those found in Omphyma from the same 

 locality, Dr. Rominger has redescribed this species as Omphyma stokesi.* 

 According to this authority, forms in all other respects similar to P 

 patellatum, from Gotland, which Zittel gives as the type,f occur at the 

 falls of the Ohio with similar processes.^ We have been able to examine 

 a few specimens of these two species from the typical localities. 



The form of corals referable to this genus is, in general, similar to those 

 of Chonophyllum and Omphyma. In P. patellatum the catyx margins are 

 often strongly and irregularly reflexed. The epithecal covering is gen- 

 erally strong and persistent. One fovea is present, at times becoming- 

 very distinct. The general structure of the corallum, as regards the 

 formation of the cell-cups and their radial infolding to form the septa, is 

 as has been described for Omphyma. We have then angular septa in the 

 outer area, gradually becoming thinner toward the center, where they 

 are twisted into a false columella and form an elevation in the calyx. 

 This columella was regarded by Edwards and Haime as distinguishing 



*Geol. Surv. Mich., vol. iii, pt. ii, 18TC>. pp 119-120. 



fHandb. der Pal., vol. i, 1880, p. 22:1. 



' 1 leol. Sun. Mich., vol. iii. i>t. ii. L876, p. 120. 



