CANADIAN PALEOZOIC CORALS. 



189 



vertical tangential sections to be made up of a series of thin, separate, 

 superimposed convex layers, of which from about eighteen to between 

 thirty and forty occur in a space of 5 mm. and between which are num- 

 erous small granules or short supporting pillars. The broad septal layers 

 as they converge become gradually more compressed laterally until they 

 form, by the bending down of their sides on each other, comparatively 

 thin, double, lamellar plates. The septa that pass down into the pit from 

 above do not apparently extend inward to the centre, but stop at the 

 bottom of the steep sides where they meet and alternate with an equal 

 number of septa that reach the centre and are there slightly twisted ; 

 how far the latter septa extend outward has not been ascertained, but 

 they do not appear on the sides of the central pit. Small, convex, 

 dissepiments arching upward and outward occur in the very narrow 

 interseptal spaces ; toward the centre of the visceral chamber they be- 

 come larger and more irregular in disposition. Of the septal layers W. 

 H. Sherzer in his monograph of the genus Chonophyllnm where an 

 accurate and detailed description is given of the complicated structure of C. 

 magnificum, says : '• Along the medial plane of each septum these layers are 

 approximately horizontal for a short distance, curve gradually downward 

 toward the sides, and finally are sharply deflected, fusing with one another 

 along their edges to form the side faces of the septum. Occasionally a layer, 

 or a series of layers, unites directly with those just beneath before reaching 

 the side, and thus takes no part, for some distance at least, in the actual 

 formation of the septal faces. When the septum has become too narrow, 

 an upper layer may send down its edges upon each side completely 

 enwrapping as many as twelve or fifteen older ones, thus suggesting their 

 method of growth. In general, these layers are not continuous from one 

 septum to its neighbour, but each septum is made up of an independent 

 series. Occasionally they pass completely across for a short distance, 

 arching upward in the interseptal cavity and assisting in the formation 

 of the vesicles." " In radial sections through the septa the cut edges of 

 these layers appear as delicate parallel lines, sloping gently from the edge 

 of the calyx downward toward the centre. Intersected at right angles by 

 the supporting growths they present, in typical forms, a Stromatopora-like 

 appearance." Epitheca complete, thin, with concentric growth markings, 

 and with narrow slightly raised lines directed toward the base, indicating 

 the position of the interseptal spaces, between which the surface is gently 

 concave. 



Localities and formation. — Corniferous limestone of Ontario ; Rominger 

 mentions its occurrence at Mackinac Island, in the drift of the lower 

 peninsula of Michigan, at the Falls of the Ohio, at Charleston Landing, 

 Indiana and in other exposures of the Upper Helderberg (Corniferous) 

 group. 



