39 
composed. The laminm, when visible, are invariably coneentric to each coral- 
lite wall, bnt often do not extend to the centre of the interstice, in which 
case a more or less nndefined narrow central space is left, common to the two 
adjoining tnhes (PI. VII, Pig. 4). This is either apparently struetureless and 
homogeneous, and free of the concentrie lines, or is occupied l)y the primordial 
wall, which, in these cases, remains in the thickened wall of sclerenchyma as 
a simple dark line (PI. VII, Pig. 3) . The median space, when structureless, 
may he, generally speaking, narrow and contracted, or, as in certain Tasmanian 
species, the frondesceiit condition of S. ovata for example, very wide. As 
regards the superficial area of these structures there does not appear to he 
any fixed rule. One or the other may occupy the whole microscopic field, or 
there may he only very limited portions of it so taken up. 
In longitudinal sections, whether of the axial or peripheral region, the 
structure, as apart from the arrangement of the periodical moniliform 
thickenings, is identical, and strictly follows the general plan of other 
Monticuliporoids, as descril)ed by Prof. II. A. Nicholson^ in peripheral sections, 
being a “ succession of superimposed conical layers of sclerenchyma, which 
are deposited one above the other as the growing margin of the wall is 
carried ujiwards.” Different appearances arc produced according to the 
position in which a corallite is sectioned. If the section runs truly across 
the centre of the corallite we simply have presented to us the thickened 
lateral peripheries of the tuhc“ (PI. VI, Phgs. 7 and 8 ; PL VII, Iffgs. 1 and 
9) ; hut if the section is taken contiguous to either the fore or aft Avail avc 
then see, in addition, a deposit of sclerenchyma also of a fibro-laminar 
structure^ (PL VII, Pig. 5), thrown into a series of folds, concaA^e doAvn- 
Avards, and thus differing from the “ superimposed layers” described by Prof. 
Kicholson. These diverse appearances are common in all good sections, and 
may ho studied in the figures referred to heloAV. In one singular section 
(PL VII, Pig. 6) the fusiform thickenings are hollow, with only the hounding 
Avails preserved. 
The chief modifications observed in the periodical thickenings of 
Australian si^ecics are the folloAAdng : — In the axial region of S. crinita (PL 
VI, Pig. 6), this being the only form in AAdiich axial swellings are developed 
Avith anything like frequency, the latter are elliptical or fusiform in outline, 
1 Genus Monticulipora, &c., 1881, p. 41. 
^ Ann. Mag. Nat. Hist., 188G, XVIl, t. 3, f. 4 & 8 : Pal. Indica, Salt Range Fossils, 1886, A^ol. I, Part 6, 
t. 110, f. Id. 
3 Ann. Mag. Nat. Hist. 1886, XA"II, t. 3, f. 10 ; Pal. Indica, Salt Range Fossils, 1886, Vol. I, Part 6, t. 110, 
f. 3 d c£' e, 
11a 50—91 G 
