14 MADREPORARIA. 
cleared our knowledge of the genus from many entanglements, but if it stays to solve all the 
questions which crop up, and will continue to crop up, it will never be finished. 
As the matter stands at present, the great bulk of the Porites, taking the inner aspect of 
the theca alone into account, seem to have the elements arranged as in Diagrams A, B, 
fig. 2. A shows an ideal vertical section, from wall trabecula to wall trabecula (w), and B is 
the ground plan of the same, with the trabecule cut across and the horizontal junctions shown 
Fic. 2.—Diagrams illustrating the structure of the theca of Porites. A, an ideal vertical 
section through a simple walled calicle of a colony; ~, the wall trabecula ; sg, the septal 
granule; p, the palus; cf, the central tubercle (these three are seen, like w, to be the 
tips of trabeculz). B, a horizontal section of a calicle in a colony in which the thece are 
slightly separated so that the synapticule joining the wall trabecule (w') with those of 
adjacent calicles (w®) have a zigzag course. C, a vertical section through a compound 
wall, which appears when the simple walls (~) are far enough apart to admit of an inter- 
vening trabecula, in this case figured as rising above the walls (w) as a wall-ridge (wr), 
making w look like another granule of the septal edge (the “wall granule”). D, an 
ideal parent calicle to explain the origin of intervening trabeculz ; they are homologous 
with costal trabecule (c), one or more of which are able to appear if the calicles in a 
colony are far enough apart to admit them ; ¢p, epithecal saucer or prototheca. 
for the most part as if complete, although those of the wall and septa are usually interrupted 
by perforations seen in the septa in A. The radial junctions seen in B are septal; the con- 
centric junctions forming the wall, and running here and there between the pali, and, again, as 
if starting, but seldom meeting, between the septal granules, are synapticular. 
This is apparently the simplest and commonest type of structure met with in Porites, so 
far as the inner aspect of the theca is concerned. And though nearly all Porites appear alike 
