PROCEEDINGS OF SECTION C. 427 



The rhizoids are not apparent in the photograph, but can be 

 discerned faintly in the specimen, though they have not undergone 

 siHcification to such an extent as the rest of the organism, and hence 

 did not etch out with the acid. 



In Plate I., fig. 2, on the left will be seen a cross section of a speci- 

 men similar to that illustrated in Plate I., fig. I. It has been etched 

 rather strongly, so that the septa and walls stand out in relief. Ob- 

 viously, therefore, the original structure is here replaced by silica. 

 The outer wall can be seen as a delicate porous investment connecting 

 the outer ends of the septa. The latter are thickened where they join 

 the outer wall, thus materially strengthening the whole structure. 

 The septa are rather numerous, indicating that the section is taken 

 through the upper and later developed portion of the calice. In the 

 upper right hand portion — where the septa are cut obliquely — the 

 pores can be made out in a few of the septa. The inner wall shows 

 very clearly the rugged porous nature of this element of the calice. 

 Stretching across the loculi can be seen (with a lens) the beautifully 

 delicate meshwork of the tabulae. In the central cavity of the calice 

 appears a mass of crystalUne calcite which has resisted the etching in 

 some degree, but does not represent any organic structure. Some of 

 the loculi also contain secondary infiltered material. 



In fig. 2 (text) the longitudinal section of one of the SelUck's Hill 

 (unsilicified) specimens is represented. It is drawn from a micro- 

 photograph, and shows very clearly the relation of the rhizoid lamellae 

 to the calice proper. As the section is somewhat oblique, it does not 

 pass quite through the bottom of the cup. At I the inner wall is cut 

 through, and the irregular projections between the pores of the former 

 are indicated. Thev may be compared in position to the rugae of the 

 perforate corals. The pores of the inner wall are well represented 

 between I and S. Crossing the loculi can be seen rudimentary dissepi- 

 mental tissue. This is very delicate and does not appear to be preserved 

 in etched specimens. 



The septa consist microscopically of granular calcite, no sign of 

 spicules being apparent. To the left of D are the pores of the outer wall, 

 which latter will be seen to merge immediately into the rhizoid lamellae. 

 This curious structure — unparalleled, I believe, in other Coelente rata — 

 resembles the septa in microscopic appearance, but contains no pores. 

 In some specimens the rhizoids seem to grow out directly from the outer 

 end of the septa, and may perhaps, therefore, be compared to enor- 

 mously developed costal ridges. The lamellae are most numerous at 

 the base of the cup, and often are not produced in the upper portions 

 of the organism. It is noteworthy that this structure is almost uni- 

 versal in the southern (Normanville, Ardrossan, Sellick's Hill) speci- 

 mens, while it is much less strongly developed in the Archaeocyathinae 

 obtained 400 miles north of the latter localities, near Beltana. 



In many of the Archaeocyathinae, however, an analogous lamellar 

 structure persists as an exothecal investment over a large portion of 

 the exterior of the cup. In Plate L, fig. 2, on the right will be seen a 

 cross section of a calice with two zones of such investment. From 

 the fact that all the buds appear to spring from a lamellar tissue of this 



