458 MR. H. 1ST. MOSELEY ON THE STRUCTURE OF THE STYLASTERIM. 
indentations in the marginal lamina, as in Allopora prof unda, corresponding with the 
centres of the outer ends of the pseudosepta. A diagrammatic view of a cyclo-system, 
as viewed from above the mouths of the pores, is given on Plate 35, fig. 15. 
The arrangement of the pores in the systems is closely similar to that in Stylaster 
densicaulis and Allopora profunda. There is a centrally-placed gastropore in each, 
which is surrounded by a ring of dactylopores with slit-like mouths. The gastropore 
in the present genus, however, appears in the form of two chambers, an upper and 
a lower, which communicate with one another by a constricted aperture. The upper 
chamber (Plate 35, fig. 8, G P) communicates with the exterior superiorly by a short 
tubular passage, bounded by the inner ends of the pseudosepta. The walls of the 
chamber are curved, so that, taken in conjunction with its upper prolongation, it is 
flask-shaped. At the base of the chamber its walls are curved inwards, so as to bound 
a horseshoe -shaped aperture, which leads to the lower gastropore chamber beneath. 
The aperture is rendered horseshoe-slraped by the projection from its margin on 
one side of a tongue-like process of calcareous matter, which is directed horizontally, 
with a slight upward curve across the aperture, reaching as far as its centre (Plate 35, 
fig. 8, B ; fig. 15, A). 
The tongue-like process is a solid calcareous structure of a bent conical form, with a 
rounded extremity. It is grooved on its under surface in the direction of its length, 
and springs from the margin of the wall of the upper chamber of the gastropore, 
which is thickened in this region by its stout roots. The process always points in 
a uniform direction, viz., in that of the length of the branch on which it is situate 
towards the tip of the branch. It thus has a similar direction to that of the lids of the 
cyclo-systems in Cryptohelia pudica. In this latter genus, a stout process of calcareous 
matter, prolonged from the support of the lid, forms a prominent ridge on the wall of 
the upper chamber of the gastropore in an homologous situation (Plate 35, fig. 7). It 
seems probable, therefore, that this tongue-like process in Astylus represents either a 
rudiment of a lid like that of Cryptohelia, which in an ancestral form protected the 
mouths of the whole of the zooids of each system, but is in Astylus withdrawn deep 
into the central cavity of the system, so as to protect the gastrozooid only ; or that 
the reverse is the case, and that the condition in Cryptohelia represents a further 
development of that seen in commencement in Astylus. 
The separation of the gastropore into two chambers by a constriction is already 
foreshadowed in Stylaster densicaulis, as has been described, by the circlet of excres- 
cences which there* form a prominent zone in the gastropore above the level of the tip 
of the style (Plate 35, fig. 3, A). 
The wall of the upper chamber of the gastropore in Astylus subviridis terminates 
below iii a thin margin, and behind the wall a cavity, continuous with that of the 
lower chamber of the pore, runs up to communicate by offsets with the tubular portion 
of the dactylopores. This cavity, in the recent condition of the coral, lodges the main 
upward-directed canal offsets of the gastrozooid. 
