94 TABULATE CORALS. 



deposition of delicate concentric laminae of sclerenchyma within 

 the interior of the corallites. The same thickening is shown 

 by the comparative remoteness of the openings of the calices 

 on the surface ; but this feature is much more conspicuous in 

 specimens in which the calices are rounded than in those in 

 which they are oblique and more closely crowded together. 

 Sections taken along the median plane of the frond (fig. i6, g), 

 and cutting the tubes longitudinally, also exhibit much-thick- 

 ened walls and correspondingly contracted visceral chambers. 

 Sections of this kind further show that complete and delicate 

 tabulae are always present, though few in number, and placed 

 wide apart, while the mural pores are few in number, large in 

 size, and quite irregular in position. Lastly, there are no traces 

 of septa to be detected, even in a rudimentary form, either in 

 tangential or in longitudinal sections. 



Formation and Locality. — Common in the Hamilton for- 

 mation (Devonian) of Arkona, Ontario ; also, rarely, in the 

 Corniferous Limestone (Devonian) of Port Colborne, Ontario. 



Pachypora frondosa, Nicholson. 



(Fig. 17.) 



Alveolites frondosa., Nicholson, Geol. Mag., new ser., Dec. II., vol. i. p. 15, 

 PI. II., fig. 2, 1874 ; and Rep. on the Palaeontology of Ontario, 



1874, P- 57- 

 Paehypora frondosa, Nicholson and Etheridge, jun., Journ. Linn. Soc, vol. 



xiii. p. 362, 1877. 

 Cladopora Canadensis, Rominger, Foss. Cor. of Michigan, p. 48, PI. XIX., 



fig- 3. 1^77- 



Spec. Char. — Corallum forming elongated palmate flattened 

 expansions, which grew in an erect position from a rooted base, 

 and which have their entire free surfaces covered with the open 

 mouths of the corallites. In size, the corallum is usually from 

 half an inch to an inch and a half in width, with a height of 

 two inches or more, and a thickness of generally two lines or 

 less. The corallites diverge from an imaginary plane midway 

 between the two flat surfaces of the expansion, and open ob- 



