200 piiOF. p. MAKTiN Duncan's jietision of tjje 



EXPLANATION OP TEEMS. 



Comllum. An entire solitary or individual coral. 



Colony. A compound corallum of authors. A number of individuals united 

 together. A number of corallites springing from a common stock. 



Corallite. An individual member of a colony. 



Common wall or colonial theca or common plateau. The structure which often 

 environs the colony at the sides, or is at the base. It may be only found 

 as a basal structure. 



Corallite-wall or Theca. The external structure which gives the corallite its 

 shape, bounds the visceral cavity and interseptal loculi, and to which 

 septa are attached within and often costse without. It is solid in the 

 Aporosa, perforated in the Perforata and in some Fungida. Walls may be 

 separate or fused together. 



Calice. The upper opening of the corallite or corallum. A calice may be cir- 

 cular, elliptical, oval, elongate, deformed, or polygonal in outline. It may 

 be separate from other caliees in a colony, or more or less united with 

 others by fusion of the walls of the adjacent corallites. The margin of the 

 calice is the top of the corallite-wall. 



The parts of the calice are— the septa, pali, the columella, the fossa, and 

 interseptal loculi. 

 Septum. A typical septum is a lamina or plate, which reaches from the inner 

 surface of the corallite-wall near or quite to the centre of the calice. It 

 may reach any distance towards a central axial line. The upper edge 

 is free at the calice, whilst the lower edge is fused with the lowest part of 

 the corallite' s cavity. 



Septa may be few in number or very numerous. They may be solid, 

 fenestrated, or perforated here and there, or reduced to mere trabecular 

 and points. They may be entire at the upper edge, or ragged and denti- 

 culate there. They may unite with their fellows laterally or by means of the 

 inner edge, but usually this is either free ; or it may be united, directly or 

 indirectly, with a columella or with pali. The spaces between the septa 

 .are interseptal loculi. 



Septa are arranged in systems, and appear in cycles or orders. A 

 typical Aporose coral has six systems, and the same number of septa in 

 each. 



The first septa which appear are the primaries, and there are six of 

 them, so that a system is between two primaries. Next come the secon- 

 daries, six in number, one between each primary pair ; so that there are 

 then 12 septa, or each system has two cycles of septa, one composed of pri- 

 maries and the other of secondaries. The tertiary septa appear between 

 each secondary and a primary, in every system ; so that there are 6 primaries, 

 6 secondaries, and 12 tertiaries, making three cycles, or 24 septa in all. 

 The next cycle has its septa in the interval between the tertiaries and 

 secondaries and tertiaries and primaries. The new septa are thereiore 4 



