7S 



BRITISH STROMATOPOROIDS. 



cessive laminae and interlaminar spaces. The result of this is to give to vertical 

 sections (PI. II, fig. 8, and PI. V, fig. 1) a singularly regular aspect, as formed of 

 rectangular spaces arranged in successive tiers one above the other. Tangential 

 sections (PL V, fig. 2) show the cut ends of the short radial pillars, and in the 

 centre of these one may sometimes observe traces of the existence of a minute 

 central cavity. The last-formed pillars terminate superficially in minute, appa- 

 rently imperforate tubercles (PI. II, fig. 12). 



In the more characteristic species of Glathrodictyon, including the type-species, 

 G. vesiculoswm, Nich. and Mur., not only are the radial pillars incomplete, in the 

 sense that many of them simply project for a short distance into the interlaminar 

 space in which they are developed, but in many cases they cease to a greater or 

 less extent to exist as independent structures. Not only do the radial pillars 

 become very irregular, but the horizontal processes which form the concentric 

 laminae are equally irregular ; and the two sets of structures are so united together 

 as to give rise to a tissue of larger or smaller lenticular vesicles. Hence in vertical 



Fig. 11. 



Fig. 11. — Clathrodictyon cellulosiim, Nich. and 

 Mur., Corniferou9 Limestone, Ontario. A. 

 Vertical section. B. Tangential section, en- 

 larged twelve times. 



Fig. 12. — Clathroiicfyon fastigiatum, Nich., 

 Wenlock Limestone, Dormington. A. Tan- 

 gential section. B. Vertical section, enlarged 

 twelve times. 



