REPORT ON CORALS—HYDROCORALLIN. 101 
Stenohelia appears to form a transition in some respects between Stylaster and 
Astylus and Cryptohelia. In it, as in the latter, all the cyclo-systems are turned 
towards one face of the flabellum, and the styles are almost or entirely wanting in 
the dactylopores ; its deep tubular curved gastropores, with their minute deeply-seated 
styles are, however, very peculiar, and characteristic of the genus. 
In Astylus and Cryptohelia the dactylozooids have come to place themselves 
out of harm’s 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 be retracted within 
their own pores, and they thus obtain a longer reach. 
The lid of Cryptohelia may he a further modification of the tongue-like process in the 
gastropore of Astylus, or the reverse may be the case, the structure in Astylus being 
a reduction of that in Cryptohelia. If the former view be correct, then the tongue-like 
process represents the scale often present in Hrrina as a covering of the gastropore, and 
the lid of Cryptohelia is a further modification of this, which is increased in dimensions 
and altered so as to cover an entire cyclo-system. 
Conopora forms a gradation to Astylus and Cryptohelia in being devoid of styles 
and in having two chambers to the gastropore, but differs from them in its irregular 
branching and the absence in it of a lid or tongue-shaped process in the gastropore. 
The phylum of the Hydrocorallinze may, therefore, be represeated as follows :— 
Archihydrocoralline. 
Archistylasteride. Milleporide. 
Sporadopora. 
| 
Ervina. Allopora. Pliobothrus. 
oe Gee ey | 
Distichopora. Lubiopora. Spinipora. Stylaster, 
Conopora. Astylus, Stenohelia 
Cryptohelia. 
