84 CONTEIBUTIONS TO CANADIAN PALEONTOLOGY. 



their distance from each other, sometimes touching ; interstitial struc- 

 ture vesicular, made up of convex plates, of rather unequal size, resting 

 on each other ; septa represented by twelve, spinose, longitudinal raised 

 ridges or carinse that appear at the slightly exsert edges of the calyces as 

 rounded tubercules ; intercalicular surface often granular or tuberculous ; 

 tabu] £8 of the corallites numerous, horizontal ; basal epitheca present. 



The genus Lyellia differs principally from both Heliolites and 

 Plasmopora by having vesicular structure between the corallites instead 

 of more or less well defined tubules. 



Lyellia affinis, Billings. 

 Plate v., figs. 1, la, 



Heliolites affinis* Billings. 1865. Canadian Naturalist, new series, vol. II., p. 427. 

 ., Billings. 1866. Cat. Sil. Foss. of Antioosti, pp. 5 and 30, fig. 12. 

 Lyellia papillata, Rominger. 1876. Geol. Sur. Mich., Toss. Corals, p. 15, pi. II., 

 fig. 3. 



The corallum of this species, as shown by the numerous specimens in 

 the collection of the Geological Survey, and as stated by Billings in his 

 original description, is hemispherical, globular, pyriform, clavato-turbi- 

 nate or tuberose ; in its earlier stages it is discoidal with a slightly con- 

 vex upper surface and flat or concave below. The smallest specimen in 

 the collection is about 16 mm. in diameter and 4 mm. thick ; it is com- 

 posed of about fifty-eight corallites, and has the base protected by a con- 

 centrically wrinkled epitheca. From larger specimens the corallum is 

 seen to attain a breadth of a little over 4 inches when hemispherical, and 

 a height of 3 to 5 inches when pyriform. Corallites circular, from 1 to 

 2 mm. in diameter with an average width of about 1 -5 mm., touching 

 each other, or at slight distances up to one-half their width apart ; some- 

 tiines when crowded they become subpolygonal. Interstitial spaces filled 

 with vesicular tissue formed of small, more or less, convex plates. 

 Tabulse of the corallites, horizontal or slightly convex or concave, from 

 two to four in a space of 1 mm. Septa twelve in number, when well 

 preserved, seen to reach about one quarter of the way to the centre of 

 the corallites. The edges of the calyces, when the surface is not worn, 

 bear twelve rounded tubercles slightly raised above the intercalicular 

 areas. 



Occurs in the Hudson River and Niagara formations, in the four divi 

 sions of the Anticosti group, and in the Lower Helderberg group. In the 



♦In the "Fossil Corals of Michigan," 1876, p. 16, Dr. Rominger pointed out that 

 Beliolites affinis, Billings, Heliolites speciosa Billings, and Heliolites exigua, Billings, 

 all belong to the genus Lyellia. 



