some Species o/" Madrepora. 189 



The wall is seen at the bottom of the intercostal spaces 

 and it is very regularly fenestrated, the openings being lai-ge, 

 longest longitudinally, and rarely circular or elliptical in out- 

 line. The solid portions of an entire space are less in extent 

 than the area occupied by the vacuities. 



The solid portions of the wall, seen at the bottom of the 

 intercostal spaces, are joined, on either side, to the base of the 

 costee, where tlie costal laminje arise from the outside of the 

 ■corallite. In most parts the costal laminae are plain at the 

 sides and solid ; but here and there a trabeculate appearance 

 is seen, owing to the existence of small arched vacuities in 

 them close to the intercostal perforations. Moreover, where 

 there are spinules on the free surface of the costje, a trabecu- 

 late appearance is given by a somewhat indefinite structural 

 connexion between the solid cross pieces of the wall and the 

 spinules at the free edge. 



It must be understood that in these descriptions the term 

 " wall " only refers to the outer layer of the mural structure, 

 which is made up of this and one or many more layers of 

 similar structure. The apical corallites have many laj'^ers 

 of wall in their mural structure, and the secondary corallites 

 have usually only one layer, or a wall, which increases in 

 tliickness at the " nariform " part. The wall is simple on the 

 corallites, remote from the nariform process, and is very per- 

 forate near the calice, the costas often projecting as trabecule. 

 The " nariform " process is not seen in many young coral- 

 lites, and it is not invariable in older secondary ones. The 

 apical calice is never " nariform." 



Frequently, and when growth appears to have been very 

 rapid, the cylindrical and rather outward-turning corallites 

 are composed of only one layer of mural tissue, and the costal 

 laminffi are almost plain at their free edges. A few very 

 small spinulose serrations or dentations are seen on the costsa 

 at some distance from the calicular margin, and some lax, 

 semi-vesicular sclerenchyma exists at and in the neighbour- 

 hood of the bases of the smaller corallites, and where they 

 arise from the axial or parent one. 



A different appearance is, however, presented on most of 

 the corallites, for exogenous growth and gemmation are very 

 common. Then there are always spinules and dentations on 

 the free edges of the costee, a little remote fi'om the calicular 

 margin, and either very distinct spinules on the surface 

 around the bases of the corallites, or the lax tissue is greatly 

 developed there. 



The spinules are larger on the surfaces around tlie bases 

 of the corallites than elsewhere, and they arc the foundations 



