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tubes. If, therefore, a distinction is to be made between the “normal” 
corallites and the “ interstitial tubes,” or “ tubules,” I fail to see why a third 
group of zooids should not be recognised, provided such zooids can be shown 
to possess distinctive features of their own. They are always larger than the 
mesopores, and usually less than the autopores, are always non-septate, and 
present in all the Australian species ; but in three of the latter, these gonopores 
are not invariably present at every fenestrule angle. They may be recognised 
by their outline, triangular or quadrangular, irrespective of position ; but the 
commoner outline is polygonal, the hexagonal predominating. Instances of 
more than one gonopore at a fenestrule angle have been observed, double as 
in the case of some mesopores, and even triple are occasionally seen, and here 
and there the geometric outline is departed from, the latter becoming 
irregular, such as longitudinally elongated, or bent in their course. Like the 
mesopores, the gonopores are liable to be filled up by stereoplasmic matter, 
and then become more or less obliterated. It may be taken for granted that 
the shorter the corallite chains the more numerous the gonopores. A good 
illustration of the hexagonal form will be found in that of II. labyrinthica, 
by Fischer-Benzon 1 ; and Pocta figures 2 a gonopore in II. catenularius , 
showing loss of outline from the deposition of secondary matter. The 
gonopores are intimately associated with the gemmation to he referred to 
later. 
9. Corallite Walls . — The walls of all the corallites vary in thickness 
in ratio to the amount of secondary alteration the tissues have undergone, 
and their condition can only he accepted in a secondary sense as a feature 
influencing specific determination. In some instances the transverse or 
mesoporal walls arc traversed by dark lines, apparently representing the 
primordial walls. When secondary silicification lias not been carried to an 
extreme extent, the walls have a fibrous appearance ; but I have not been 
able to distinguish a similar difference in structure to that described by 
Sardesson 3 between the fenestrule, or main walls, and the transverse or 
mesoporal walls. When secondary silicification is carried to its most extreme 
condition, the walls, particularly the main or fenestrule, are more or less 
entirely destroyed by conversion into chalcedonic blebs. 
10. Septal Spines . — These have been detected in five of our forms, 
and are thorn or spine-like protuberances extending into the visceral chambers 
for variable distances. The cycles between any two tabulae vary from two to 
three, and in only one instance have I been able to satisfactorily count the 
1 Fischer-Benzon, Abhandl. Gebeite Naturwis. Verein Hamburg, V, 2 Abth., 1871, pi. 1, f. 9. 
2 PoCta, Barrande’s Syst. Sil. Boheme, VIII (ii), 1902, pi. cxvi, f. 5. 
* Sardesson, Neues Jahrb. Min., Beil.-Bd. X, 2 Heft, 1896, p. 273. 
