REPORT ON CORALS — HYDROCORALLIN.-E. 67 



;i 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 

 cyclo-systems in Cryptohelia p>udica. 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 II. 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 mouths of the whole of the zooids of each system, but is in Astylus withdrawn deep 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 (PL II. 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 intervening between the dactylopores are, 

 in origin, double laminae, as in Stylaster densicaulis, but in the present form appear 

 as thin plates, which have so regular a radial 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 



