31 
his II. regularise and H. eschar oides, 2 and by Nicholson again in the latter 
species. 3 They approximate closely to one another towards the caliciual 
centres, but in only one instance could I detect any union, and then only of 
two opposite spines without the formation of a longitudinal pseudo- 
columella. The number of cycles to a visceral chamber is also variable, one, 
two, or three, according to the distance apart, of the tabulae. 
I also referred to the proximity to one another of the autoporal tabulae, 
and the comparative distance apart of those in the mesopores. The latter 
statement holds good ; but the former character in this species, like that of 
the spinifonn septa, is open to much variation, even in the same corallite. 
The autoporal tabulae may be quite close, from five to six in the space of one 
millimetre, or distant, three being contained in the same space. This, 
although in words a very trivial matter, is in reality an important feature, 
and presents in a section a most marked difference to that exhibited by the 
more numerous tabulae. Another peculiarity is that patches or clusters of 
the closely-set, tabulae may appear in a group of corallites as the fundamental 
character of that particular series, and in consequence, several longitudinal 
sections are necessary, should the observer suspect ho is examining a specimen 
of II. australis, before absolute certainty can be arrived at. Once this dual 
structure of the tabulae in the autopores has been observed, the distinction I 
formerly drew between II. australis and other species still holds good. 
Gonopores, as in II. cratus, are not invariably present at the junction 
of corallite chains, although the absence of this particular form of zooid from 
its normal position is not common. 
The special points that appear to distinguish H. australis arc — 
(1) rambling form of growth ; (2) comparatively large size of the fenestrules ; 
(3) thickness of the autoporal walls ; (4) variability in the distance apart of 
the autoporal tabulae ; (5) pipe-like form of the mesopores in longitudinal 
section; (6) length of the spinifonn septa, and their tendency to unite at the 
calicinal centres; (7) occurrence of a septal spine on each auto-mesoporal 
wall. 
The lax and loose rambling habit of this coral is very like that depicted 
by Mr. R. Etheridge in his H. catenularius, var. Harti , 4 from the Arctic 
Regions. In fact, his remarks on the variety named apply equally well, so 
1 Fischer-Benzon, Abhandl. G-ebiete Naturwis. Verein Hamburg, V, 2 Abth., 1871, pi. ii, f. 3. 
2 Fischer-Benzon, I hid. , pi . iii, f. 2. 
1 Nicholson, Tab. Corals Pal. Period, 1879, pi. x, f. G. 
4 Etheridge, Quart. Journ. Geol. Soc., 1878, XXXIV, p. 583, pi. xxviii, f. 2. 
