22 MADREPORARIA. 



for Goniopora at all. The majoi'ity of the figures will show how completely it is, as a rule, 

 obscured, and I had not at that time discovered the tendencj^ of the lateral calicles to revert 

 to the primitive type (see below on the Growth-forms). • 



The directive septa are frequently reduced (cf PL IV. fig. 9 ; in the uppermost calicle the 

 plane of symmetry runs across the page, the right-hand directive is reduced, but in the lowest 

 right-hand calicle the plane runs xij) the page, and both directives are complete). There may 

 be a flattened central tubercle to indicate the directive plane, or else one of the directives 

 may be greatly prolonged. 



The upper and inner edges of the septa are denticulate, this being merely an expression 

 of their perforate character.* This perforation may go so far as to reduce the septa to mere 

 thin filaments : cf. the specimen described on p. 68 as G. Philippines t2, and for others see 

 Table IV. p. 180. 



The taller the wall naturally the steeper is the slope of the septa into the deep fossa. 

 There is some correlation between this depth and the formation of pali. Deep funnel-shaped 

 calicles show only slight development of these structures ; they may be nothing more than the 

 thickening of the edges of the principal septa (as in the upper calicles, fig. 5, PI. VIII.) Deep 

 cylindrical calicles, on the other hand, usually have pronounced pali, but feebly developed 

 septa. It is common for such steep cylindrical walls to show hardly any trace of septa 

 round their margins, and only deep down the principal septa suddenly project and, bending up, 

 rise as plate- or rod-like pali high in the fossa. Both these types of calicle, however, tend, as 

 we shall see, to pass gradually at the sides into the same primitive regidar type with central 

 rosette. The ragged inner edges of the septa always fuse in the centre to form : — 



The columellar tangle : this is always present, but is obscured in deep funnel-shaped 

 calicles. In these it usually consists of a loose tangle of filaments formed from the edges of 

 the septa, but it tends to become a well-defined structure filling up a conspicuous place in 

 the floors of shallow calicles. When well developed it frequently so involves the septa that 

 their typical arrangement is quite obscured, and they are reduced to mere connecting pieces 

 between columellar tangle and wall. The pali then no longer appear as upturned portions of the 

 septa either singly or fused together, but, if at all, as raised portions of the columella. It is some- 

 times possible to trace a V-shape in them due to theu' origin at the points of fusion of the septa. 



The pali : these are typically six in number, see above, diagram A, p. 21. Then- chief 

 variations have just been mentioned in describing the septa and the columellar tangle 

 (see further, p. 145). The somewhat surprising fact, tliat the pali are associated with the 

 secondaries rather than with the primaries has been already noted. 



The tabulcB : these structures are very conspicuous in this genus and play an important role 

 in colony formation. They are mere repetitions of the primitive epitheca, but no longer in 

 contact with the substratum, being secreted instead as an intraskeletal plate shutting off' that 



* In fossils the top edges of the septa are frequently shown as moniHform, e.g. Pmites indica, in 

 Duncan's ' Sind Fossil Corals,' pi. v. fig. 1 2. But these are in most cases due to post-mortem altera- 

 tions of the skeletal substance. 



