1899] Lam BE — Canadian Palj!;ozoic Corals. 223 



Corallum large, circular, much broader than high, expanding 

 laterally from a small, obtusely pointed base into a broad thin, 

 frill-like horizontal extension above whose upper surface rises 

 abruptly a central calicular area about one-fourth the breadth 

 of the corallum ; attaining a breadth of over 19 cent, and a 

 thickness at the centre of about 4 cent. Height of the central part 

 enclosing the calyx, above the level of the surrounding surface, 

 in large individuals, from about r5 to 2 cent. Calyx* about 

 twice as wide as high, with a diameter of about one-tenth the 

 breadth of the corallum, flat at the bottom with very steep sides. 

 Septa, in the visceral chamber, lamellar, of two orders, primaries 

 and secondaries, alternating, the former meeting at the centre with 

 a slight amount of twisting, the latter not quite half the length of 

 the former ; ascending the sides of the calyx as sharp-edged 

 lamellae they pass down and over the extracalicular surface as 

 gradually broadening, flatly convex, radiating ridges having a 

 maximum breadth near the periphery of 7 mm. ; they number 

 in different individuals from about seventy-four to eighty-four. 

 Well developed flat or concave tabulae, turned down at their 

 edges and as broad as one-half the width of the calyx, are seen 

 in a radial section, beneath the bottom of the cup. The whole 

 of the upper surface is marked by fine, raised, interrupted and 

 concentric, ripple-like growth lines, generally less than i mm. 

 apart, those of one septal ridge sometimes continuous with at 

 other times alternating with those of adjacent ones ; the 

 basal surface presents a similar appearance except that here the 

 septal radii are concave instead of being convex The structure 

 of the walls of the calyx and of the extended frill-like margin 

 appears to be very dense. In radial sections the gradual growth 

 of the corallum outward is indicated by parallel lines approxi- 

 mately at right angles to, and joining the ripple-like markings on, 

 the upper and lower surfaces. In vertical tangential sections the 

 septa are seen to be made up of superimposed convex layers 

 resembling the septal structure of C. niagnificum, Billings, but 

 denser. 



*Originally described as the basal centre "excavated inio a cup-like cavity." 



