406 Dr. R. Schéfer—On Phillipsastrea, d’ Orb. 
The space which in the living animal would exist between the — 
tabula and the vesicles in the interseptal loculi, becomes filled 
up by a stony matrix in the process of fossilization. In weathering 
this stony mass offers less resistance than either septa, tabule or 
endothecal sclerenchyma. Accordingly the appearance which the 
corallum presents after the surface has been weathered depends 
largely on the original structures. 
Where the tabule are conical and bent upwards, the weathered 
surface appears mammillated, whilst the surface is almost flat where 
the tabule are more horizontal. Since gradations exist between the 
different kinds of tabula, we must expect to find on the surface 
of weathered specimens all varieties between smooth and mam- 
millated calyces. It seems to me impossible to consider the 
specimens with a mammillated calyx as of a distinct species from 
those with a flat calyx. On Pl. XII. Figs. 1 and 2 I give an illus- 
tration of two specimens, of which one, Fig. 1, shows a smooth 
surface, whilst the other, Fig. 2, appears somewhat mammillated ; but 
in other parts of the same specimen the surface of the calyces appears 
smoother. The bearing of this fact on the specific distinction 
between Phillipsastrea tuberosa and Phillipsastrea radiata is obvious. 
Minute structure of the septa, the vesicles, and the tabule.—The 
state of preservation of the specimens examined by me was very 
favourable, and allowed me alse to study the minuter details in the 
sections. 
The septa are formed of bundles of calcite fibres, which lie on 
either side of the median plane of the septum. From this starting 
point on this plane each fibre passes upwards and outwards in the 
direction of the proximal end of the septum. ‘Thus a feather-like 
structure is brought about in the sections, which reminds one of 
that which Pratz' has described and figured for Thamnastrea. 
Pl. XII. Fig. 8, shows this structure in horizontal section, whilst in 
Pl. XIL Fig. 9, may be seen the same in vertical section. Examined 
by polarized light, with crossed Nicols, the single calcite fibre shows 
straight extinction, that is to say, becomes dark when by the turning 
of the stage the fibre is parallel to the principal section of each Nicol. 
Hence it arises that each single calcite fibre is a crystallographic 
individual. The vesicles and tabule differ from the septa, but 
resemble one another in histological structure. This proves that 
in the living animal the vesicles and tabula were produced in the 
same manner. When viewed with a higher power they do not 
become transparent, but always remain opaque. Under a still 
higher power they occasionally appear separated into heaps of fine 
granules. 
The difference of structure between the septa on the one hand, and 
the vesicles and tabule on the other, arises chiefly through their 
having originated in a different manner in the living animal. If we 
consider that as the living animal grows upwards it secretes the 
1 E. Pratz, Ueber die verwandtschaftlichen Beziehungen einiger Korallen- 
gattungen mit hauptsachlichster Beriicksichtigung ihrer Septalstructur. Palzeon- 
tographica, vol. xxix. p. 81, pl. xiv. fig. 12, Cassel, 1882-1883. 
