lAMBE. ] CANADIAN PALjEOZOIC CORALS. 107 



MiCROCTCLTJS DISCUS, Meek and Worthen. 



Microcyclus discus. Meek and Worthen. 1868. Geol. Surv., Illinois, vol III., p. 420, 

 pi. XI., figs. 7, a, I. 

 II >i Nicholson. 1874. Palseou. of Ont., p, 39. figs. 9a, 96. 



Corallum simple, small, discoidal with a thin periphery, varying in 

 diameter from 4 to over 15 mm., and generally not more than 9 mm. in 

 maximum thickness, somewhat convex above, flat or convex below, 

 adherent by part of the lower surface to foreign objects such as very 

 small shells, fragments of crinoidal columns, etc. Epitheca complete, 

 covering the basal surface, concentrically marked by irregular accretion 

 ridges and by very fine close-set lines of growth with sometimes slight 

 indications of radial septal furrows. Septa numbering from about thirty- 

 six to forty-eight, thick, in the form of convergent, somewhat angular 

 ridges on the upper surface, of two sizes, alternating, the primaries pass- 

 ing a little more than half way toward the centre, the secondaries only 

 about one-third the length of the primaries. Middle of upper surface 

 smooth, generally slightly concave. Fossette, comparatively deep, con- 

 spicuous, narrow, extending from near the centre toward the margin, 

 where it is occupied by one septum. A constriction of the calicular sur- 

 face seems to be not uncommon and results in a slight thickening of the 

 corallum. Not infrequently a coalescence of two or three primary septa 

 or of the secondary septa with the primaries takes place, giving the septa 

 the appearance of bifurcating or trifurcating. In a vertical section 

 through the corallum no tabulae nor dissepiments are apparent. 



Meek and Worthen in their description of the species mention a breadth 

 attained by one of their specimens of 0-77 inch with a height of 0-15 

 inch. 



Localities. — Not uncommon in the Hamilton formation of Ontario ; 

 collected by the Re/erend H. Currie in 1882 at Widder, Ont. and by Dr. 

 Whiteaves on the Sable River, Ont. in 1891. 



ZAPHRENTID^. 



Genus Streptelasma, Hall, 1847. 



Streptoplasma, Hall, 1847. Palaeon. New York, vol I., p. 17. (Changed in explanation of 

 figures to Streptelasma.) 



Corallum simple, conical. Epitheca complete. Calyx generally of 

 moderate depth. Septa numerous, well developed, their outer ends com- 

 bining to form a thickening of the thin wall proper ; of two sizes alternat- 

 ing, the larger twisted at the centre, the secondaries usually embedded 

 in the thickened wall or projecting only slightly from it. No true tabulae 



