194 MADREPORARIA, 
This specimen is greatly altered: it is hard, solid and crystalline, and again shows the 
same two methods of disintegrating. In parts the walls disappear and leave solid prisms 
running up through the mass, and in others the intra-calicular skeleton decays and the walls 
persist, thick and solid. In the microscopic section there seem to be clear traces of a boring 
alga having hollowed out the skeletal elements here and there, very irregularly, and it is 
known that such boring alge do at times confine their operations to walls, sparing the septa 
(see Vol. IV. p. 53). I have not, however, seen a case before in which they attacked the 
septa and spared the walls. 
There are the two halves of the original specimen (No. 306), and two portions of the 
slice out of which the microscopic slide was prepared. 
a. Geol. Dept. R. 3730. 
With this may be placed— 
No. 609.* 
[South of Flying-Fish Cove. | 
Syn. Porites belli (pars) Gregory, 1. ¢. fig. 6. 
This is a large solid block, showing the same differentiation of the fossil mass as the last ; 
only here and there, as in the part illustrated by Dr. Gregory, the skeleton is better preserved. 
The wall can be seen intact, and here and there thickened into a regular reticulum, that 
is by the formation of an inner synapticular wall, especially in the angles and spaces between 
the circular calicle and the nearly straight polygonal walls. Traces can also be seen of a 
ring of skeleton round the fossa. The radial symmetry of the septa is not very pronounced, 
The microscopic slide shows well the ravages of the boring alga. Professor Gregory 
makes this remark of his fig. 7; but the real section of No. 853, which fig, 7 is intended to 
illustrate, is very difficult to understand, and while it does show the boring of the alga, the 
method of fossilisation has obscured the details in a way which I have not yet succeeded in 
unravelling, 
There is one large block, and two portions of the slice from which the section was prepared. 
In connection with this specimen, cf. ‘A Monograph of Christmas Island,’ p. 295, with 
fig. 4, p. 275. A gigantic mass of Porites between 20 and 30 ft. high is described by 
Mr. Andrews as exposed in this sea cliff. It may have been of the same kind as this, 
b. Geol. Dept. R, 3748. 
* Some confusion has crept into Professor Gregory’s paper. His fig. 6 is said to refer to 
No. 609. This is correct; but No. 609 is accidentally given as No. 6 in his text. Then again 
it is stated that his fig. 7 refers to No. 6 of his text, but his No. 6 is a mistake for No. 609. It 
really refers, as the labels show, to No. 853. The method of illustration adopted is unfortunate, 
confusing rather than illuminating. (See Vol. IV. p. 120.) 
