1.5-6 TABULATE CORALS. 



are also often serrated with erect spinules, which appear to 

 represent continuations of the septa towards the axis of the 

 visceral chamber. New corallites budded forth between the 

 old calices from the hollow connecting-floors. 



The dimensions of the corallites, the degree to which they 

 are in contact, and the closeness of the periodical expansions, 

 vary in different examples. In the most typical forms, the 

 tubes themselves are about two lines in diameter, but the 

 diameters of the polygons inscribed round these upon the upper 

 surfaces of the horizontal floors (where recognisable) are three 

 lines or more. In other examples the tubes themselves may 

 reach three lines or over in diameter. The periodical expan- 

 sions which give rise to the horizontal floors by their union are 

 mostly from one line to a line and a half distant from one 

 another, but they may be two or even three lines apart. The 

 corallites are often only from half a line to a line apart in their 

 constricted portions, but they may be distant two, three, four, 

 or even five lines, and, on the other hand, they generally ap- 

 proach one another in parts of a large colony, so as to become 

 closely contiguous or coalescent. 



Obs. — It is not necessary to add anything to the above de- 

 scription of the general characters of this singular species (PI. 

 VIII., figs. 2-2C). I may, however, shortly describe the ap- 

 pearances presented by thin sections, by which alone the internal 

 anatomy can be satisfactorily studied. The most instructive 

 sections are vertical ones (PI. VIII., fig. 2 c), which admirably 

 exhibit the alternately and rapidly constricted and dilated tubes 

 of the corallites, each of which looks like a series of wide and 

 shallow funnels arranged in vertical order. These sections also 

 show the important fact that the periodic expansions of the 

 tubes are really hollow prolongations of the visceral cavities of 

 the corallites, so that by the union of these to form the hori- 

 zontal connecting-floors all the polypes of the colony are placed 

 in actual organic connection. The tubes are traversed by well- 

 developed, arched, flexuous, or nearly horizontal tabula;, the 

 upper surfaces of which commonly carry short erect spines, 



