204 MADREPORARIA. 
latter are often the deeper. The wall varies greatly. It is frequently—e.g. on the growing 
tops of stocks—very thin, zigzag, incomplete, and ragged. The angles between calicles are 
nearly always thick and reticular, and raised buds are frequently to be seen upon them. 
Down the sides the walls are thicker, and may become reticular, and in two ways: we may 
have either a more or less regular filamentous reticulum with persistent septal symmetry, or 
a very ragged, flaky reticulum, not very thick, but with the septa running out as narrow, 
jagged, and twisted flakes, the septal system then forming an irregular reticulum across the 
calicle. Again, on still lower parts the wall may be a thick, solid mass of granules, and the 
septal system also a compact mass of granules when seen from above. 
The septa are very thin, straight, and regularly arranged in the thin-walled calicles ; their 
edges are irregular, but septal granules and pali appear in all degrees of conspicuousness. 
Where the septal system is an irregular network, these latter are not developed at all; but 
where the walls are filamentous, they depend upon the thickness of the elements, and may 
be regular rings of knobs or flattened plates visible to the naked eye, or almost vanishing 
points quite irregular in their appearance. The distance between the septal granules and pali 
may be large enough to make the latter appear as a central boss standing up from the floor of 
the shallow calicle. When the elements are thickest, the two rings of large granules, with 
the larger central tubercle, may fill up the whole calicle. 
In the ordinary calicles the central tubercle is frequently deep down and obscure. 
The section shows a fine, dense arrangement of thin trabecule, separated by comparatively 
large, round pores, but all small and delicate. The sheaf-like arrangement of the trabeculz in 
the formation of the knobs and columns may be conspicuous; even a solid block may be seen 
in section to consist of a compact mass of such sheaves, each of which, however, forms an 
eminence on the top surface. The colour is a brown or fawn. 
In this group are some of the finest specimens in the collection. 
a. Was originally attached to a decayed Favia, from which its base spreads out laterally 
on all sides, 7 to 15 cm. The sides ascend steeply and smoothly for 24cm, Assuming that 
column formation is the principle of structure, we may note that in this form they were large, 
thick, and smooth. They are fused so compactly that the sides of the stock are fluted, as much 
as 3. cm, deep and 7 cm. apart on one side, the flutings standing out as blunt keels, which, 
however, may break up into so many separate knobs or eminences. 
The calicles on the flat top, which shows only slight traces of the column formation, are 
all with thin, incomplete, zigzag, filamentous walls. There are a great many double calicles, 
among which, now and again, as many as four calicles fused in a row may occur. 
The base of b rests upon quite a small mass of a previous growth, a vertical section of 
which shows that the mass consisted of a dense cluster of sheaves of trabeculz, the top of each 
sheaf forming a rounded knob at the surface. Above the base, which is nearly 40 cm. across, 
and with its thick, turned-out, cushion-edge, the mass rises into a truncated cone of erect, flat- 
topped columns all fused together below, but with their tops often 6 cm. or more as free 
projections. Each column is itself covered with slight bulgings, as if they were the beginnings 
of a similar column formation. 
c. Is much smaller than either a or b. Its sides are more nearly vertical, like those of a. 
