REPORT ON CORALS—HYDROCORALLIN A. 67 
a uniform direction, viz., in that of the length of the branch on which it is situated 
towards the tip of the branch. It thus has a similar direction to that of the lids of the 
eyclo-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 a homologous situation (Pl. IL. 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mouths of the whole of the zooids of each system, but is in Astylus withdrawn deep 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 (PI. Il. fig. 3, A). 
The wall of the upper chamber of the gastropore in Astylus subviridis terminates 
below in 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. 
The lower chamber of the gastropore is a cavity with a rounded bottom, which is 
excavated within the substance of the branch supporting the pore system. The cavity 
communicates with the upper chamber by the horse-shoe shaped opening, and with 
the dactylopores as already described. With adjacent cyclo-systems it communicates 
by means of the axial canals of the branches. There is no trace of a style at the bottom 
of the gastropore. 
Around the mouth of the gastropores the mouths of the dactylopores appear as 
elongate slit-like openings, radially directed towards the axis of the systems. The outer 
peripherally-placed margins of these slits are rounded, whilst internally the slits join the 
cavity of the gastropore. The pseudosepta intervenmg between the dactylopores are, 
in origin, double lamine, as in Stylaster densicaulis, but in the present form appear 
as thin plates, which have so regular a radia] arrangement and so wide an extent that 
they simulate the septa of Hexactinian corals more closely than do those of any other 
Stylasterid. 
The inner extremities of the summit borders of the pseudosepta by their arrange- 
ment form a circular aperture leading to the cavity of the gastropore. There are from 
eighteen to twenty-one dactylopores in each cyclo-system. The upper wide slit-like 
chambers of the dactylopores are continued into small short tubular cavities below, as 
in Stylaster densicaulis; but these are entirely devoid of a style. The mouths of 
