MADBEPOEAEIAN FAMILY — THE TUNGHDiE. 145 



base, relate to the incoming of new septa, and fill up with age. 

 Here and there the costse are united by a synapticulum which 

 stretches across from the flank of one to its next neighbour. 

 Piually, the minute spinulose ornamentation of the sides of the 

 septa is seen between the synapticula ; and it is evident that they 

 are difterent things. 



Memarhs on the Distribution of the Septa. — The thinnest and 

 smallest septa (on either side of the medium septum in alternate 

 large interseptal loculi) overtop those between them, and arch 

 oyer them in the form of a finely trabeculate tissue in some 

 places. And midway towards the axial space these more delicate 

 septa unite to form a thick one, and this in its turn unites 

 nearer the axis with another one formed in the same fashion. It 

 is near those junctions that delicate trabeculse cross the spaces 

 between the smaller septa and act as synapticula. The thickening 

 near the upper part of the synapticular ridges is seen in the smaller 

 as well as in the larger septa. 



If two of the thickest and tallest septa which are nearest each 

 other at the axial space be considered limits of a system, there 

 will be a large aud slightly smaller one between them at the axis. 

 There are primary interloculi between them. There are three 

 very small septa in such an interloculus — that is, between each 

 large septum and the smaller median one ; and they reach, after 

 uniting as one, close to the axial space. 



The three larger septa do not have others joining them ; and 

 they pass to the margin, diverging considerably so as to admit 

 of the origin and junction of many smaller septa ; and these in- 

 crease in size towards the margin according to their age or origin 

 near the axial space. The three septa in each primary interseptal 

 loculus reach the margin as thick ones ; and so many are added 

 towards and in the outer half of the coral between the two large 

 septa, that no less than forty can be counted there. 



The larger septa project beyond the smaller at the margin of 

 the corallum ; and every septum is continuous with a costal ridge 

 which is denticulate, except in the instance of the very short costse 

 of the latest and minutest septa. About thirty large septa reach 

 the axial space which they bound. 



The young septa originate between the next older ones, or 

 between a next older one and a much older one. They com- 

 mence at the base; aud it appears that synapticula are formed 

 either prior to or simultaneously with the septum, for they and 



