280 W. H. SHEKZER — THE GENUS CHONOPHYLLUM. 



reflexed calicinal margins, leaving a monticulose rim around the central 

 pit. The fovea is obsolete or merely indicated. A thin epithecal cover- 

 ing is present which shows the broad bands and narrow grooves arranged 

 as in Omphyma and Ptychophyllum. The septa, as seen in the calyx, are 

 thin about the pit but broad and angular in the outer area. They are 

 <>t' two orders, the secondaries terminating at the pit and the primaries 

 reaching the center without any decided twisting. Cross-sections show 

 these septa to be thin and lamellar, becoming nexuous and ill defined 

 in the outer area. In this region they are at times strongly earinated. 

 the lateral plates either in corresponding position on opposite sides of 

 the same septum or alternating in position. Vertical tangential sections 

 show the thin, fiexuous septa with delicate plates arching downward 

 from each side to the center of the interseptal cavities, generally placed at 

 the same height on opposite sides of the same septum and giving an ap- 

 pearance suggestive of the Chonophyttum septal structure. Considerable 

 irregularity occurs in these layers and. at times, continuous horizontal 

 plates are introduced which may be traced across a number of septa, in 

 radial sections these plates give with their cut edges a series of parallel 

 lines curving upward and outward from the center, while the coarser 

 carinse cross them at right angles downward and outward from the 

 center. A well defined vesicular structure occurs in the 1 »r< >ad interseptal 

 cavities. The tabulae are poorly developed through the central area. 



It may be distinguished from Chonophyttum then by the following 

 points of structure : 



1. The lamellar septa. 



2. The much broader interseptal cavities. 



3. More complete tabulae. 



4. The carinal structures. 



•5. The broad longitudinal ridges on the epitheca representing the 

 position of the interseptal cavities and the narrow lines the septa them- 

 selves. 



6. The general form of these corals distinguishes them from all species 

 except 0. pseudohelianthoides. 



Horizons and Distribution. 



The only known European forms are C. perfoliatum and C. ]>■« udohi li- 

 anthoides. Goldfuss' specimen of the former is from the Upper Silurian 

 (Niagara) of the island of Gotland, while Edwards and Haime's speci- 

 mens were collected from the Devonian rocks of Brulon, France, and 

 Torquay. England. The latter species is from the Upper Silurian of 

 Conjepruss, Bohemia. The remaining species are entirely American, as 



