484 MR. H. N. MOSELEY ON THE STRUCTURE OF THE STYLASTERIM. 
the pores are found to he in all the systems still entirely independent (fig. 12), and 
this condition is maintained at greater depths in all Stylasters. 
In Astylus and Cryptolielia the tentacular zooids have come to place themselves 
out of harms way, not by retraction within their pores, but by being doubled down 
within the gastropore, which is divided in two chambers. They are thus enabled 
to maintain a greater length than they could were they obliged to he retracted within 
their own pores, and they thus obtain a longer reach. 
Allopora Madeirensis (Johnston) forms a gradation towards Astylus and Crypto- 
helia in that it has its cyclo-systems all turned towards one face of the flabellum, but 
differs in having styles in the gastropores. The lid of Cryptolielia may be a further 
modification of the tongue-like process in the gastropore of Astylus, or the reverse 
may he the case, the structure in Astylus being a reduction of that in Cryptolielia. If 
the former view be correct, then the tongue-like process represents the scale often 
present in Errina as a covering of the gastropore, and the lid of Cryptolielia is a fur- 
ther modification of this which is increased in dimensions and altered so as to cover 
an entire cyclo-system. It is to be noted that in becoming so remarkably modified 
into elongate slit-like cavities, the dact-ylopores of Stylasteridse, with cyclo-systems, 
follow an ancestral tendency to modification, for these elongate pores are, taken sepa- 
rately, closely similar in form to the nariform dactyl opores of Errina and its allies. 
They only have the bps of all the projections directed radially outwards. 
From the appearance of rudimentary cyclo-systems in the pore rows of Distichopora, 
it seems probable that this genus represents an extreme modification of those 
Stylasters in which the systems are confined to the sides of the branches of the 
flabellum, closely opposed cyclo-systems having degenerated into a triple row of j:>ores, 
in which the gastropores occupy the central row of the three (Plate 35, fig. 16). 
The phylum of the Hydrocorallinse may, therefore, be represented as follows : — 
Archihydrocorallinse. 
Archistylasteridse. 
Milleporidse. 
Sporadopora. 
Errina. 
Alio 
Labiopora. Spinipora. 
Dora. Pliobothrus. 
Stylaster. 
Astylus. 
I 
Cryptolielia. 
Distichopora. 
