102 PEOF. P. MAKTIIS^ DUTTCAlSr Q-R THE 



The calices and their margins at the upper ends of the corallites 

 the sides and walls of which have just been noticed, are slightly 

 worn down. The outlines of the transverse views of the corallites 

 thus given are more or less polygonal, and the walls between the 

 lumina of neighbouring corallites are very narrow, and are insepa- 

 rable, being perfectly united (fig. 2). In some instances the united 

 walls are not thicker than one of the slender septa, and are even less 

 than one tenth of the diameter of a corallite ; in others the thickness 

 is greater, but at this place in the corallum it never amounts to 

 one third of the diameter. Where the state of preservation is good 

 the crowding of the corallites and their thin walls, represented by 

 white mineral, are very striking, and recall the parts of some 

 modern corals when growing unusually quickly. The columella is 

 moderate in size, styliform, and fairly circular in exact transverse 

 section. The septa are remarkably thin, and in some places almost 

 linear, in others they are moderately stout. The longer septa are 

 variable in number according to the size of the corallite, and there 

 may be eight, nine, or ten of them. The smaller septa are placed 

 between the larger, and do not reach far inwards. 



The surface of a polished transverse section of the colony made at 

 the depth of an inch from the free surface, presents many scores 

 of corallites, some cut transversely and others more or less obliquely 

 to their long axes. The details of the corallites are wonderfully pre- 

 served, and one cannot but be struck with the manner in which the 

 ancient crowding of the corallites has been rendered apparent by 

 the variation in the calibre of the insides, and in the varieties of the 

 polygonal outlines retained by the sections of the different indi- 

 viduals (fig. 3). 



The shape of the corallites in transverse section is very different 

 in the several parts of the section of the colony. The portions 

 of the section which are evidently transverse and not oblique 

 show polygonal shapes, the lumen often being circular. 



The shapes are often quadrangular, sometimes pentagonal, fre- 

 quently hexagonal, and rarely triangular. The quadrangular shape 

 occurs in lines, and the other forms evidently depend upon irregular 

 pressure during upward growth. Yery deformed corallite sections 

 relate to budding individuals and to those which have just become 

 independent of the parent. 



The diameter of the corallites varies from 1-25 mm. to 2-25 mm., 

 and these measurements refer to corallites which have their full 

 septal number ; one half of the dense tissue between the lumen 

 of one corallite and that of its neighbour is included in the mea- 

 surement. This one half represents the proper mural tissue of a 

 corallite. The thickness of the wall of the corallites measured 

 above is one eighth of a millimetre and one twelfth of a millimetre. 

 Thus the structure intermediate between the inside or calibre of 

 two neighbouring corallites is one quarter or one sixth of a mil- 

 limetre wide. In some parts, however, the width of the united walls 

 may be nearly or quite equal to that of the calibre of a corallite 

 (figs. 4, 5). 



