GENERA OF FA VOSITID^E. loi 



pora, being in the form of deep cups, surrounded by thin poly- 

 gonal margins, with a much smaller rounded or oval aperture 

 at the bottom, leading into the visceral chamber. Tangential 

 sections taken close below the surface (PI. V., fig. 2 c) show 

 that the throat of the tube is beset with a variable number of 

 radiating spines, representing the septa ; and similar structures 

 may often be detected within the tube-cavity itself. Transverse 

 sections (PI. V., 2 b) show (like the preceding) that the walls 

 of the corallites are immensely thickened by numerous delicate 

 concentric laminae of sclerenchyma deposited in their interior ; 

 and they are specially instructive as exhibiting the varia- 

 tion of the amount of this secondary deposit in different 

 parts of the corallites. Thus, in the centre of such a section 

 the vertically - placed tubes in the axis of the branch are 

 cut across at riofht angles, and here their diameter is com- 

 paratively small, and the extent to which they are filled up is 

 less. On the contrary, the outer portion of such a section cuts 

 obliquely through the corallites in the terminal part of their 

 course, just as they curve outwards to open on the surface. At 

 this point, therefore, the tubes are seen to be considerably ex- 

 panded, and a proportionately large amount — generally about 

 two-thirds — of the actual space comprised within the proper 

 walls of the corallites is here filled up with sclerenchyma. 

 Vertical sections (PI. V., fig. 2 d) show the general course of the 

 tubes, and also the same progressive thickening of the walls 

 as the mouth is approached. They show at the same time 

 that the proper walls of the corallites never become obliterated ; 

 that the visceral chamber is crossed by remote, delicate, hori- 

 zontal, and complete tabulae; and that contiguous tubes are 

 placed in communication by comparatively abundant circular 

 mural pores, which in all respects appear to resemble those 

 of Favosites itself, except that they appear to have a quite 

 irresfular distribution. 



Formation and Locality. — Rare in the Hamilton group 

 (Devonian) of Arkona, Ontario. 



