REPORT ON CORALS—HYDROCORALLIN %. 57 
not allow of such retraction. No doubt the zooids, when active and expanded, are 
long and attenuated, and the long spines on which they are borne are very possibly to 
be regarded as contrivances for giving them a long reach. A tendency to attachment 
by the side of the base, within the zooid pore, has been already noticed as occurring in 
the dactylozooids of Sporadopora dichotoma.! It is here the normal condition, and 
much more fully completed. <A closely similar method of attachment and retraction of 
the dactylozooids occurs in all the genera of Stylasteride which form regular cyclo- 
systems of zooids, 
The smaller dactylozooids are simple bluntly-conical bodies of less than one-third 
the size of the larger form. They occupy the smaller dactylopores, and are retracted 
directly within these when at rest (Pl. V. DD). 
Gastrozooids.—These are cylindrical in form, with a dome-like hypostome and six 
apparently simple conical tentacles set on in a single whorl. The zooids are, as usual, 
retracted within sacs lining their pores. The tentacles in the retracted condition of the 
zooids are doubled together over their hypostomes, with their tips bent inwards and 
downwards towards them. The zooid bases terminate in four large canals of the 
coenosarcal meshwork, and are firmly united to the styles of the pores. 
Gonophores—No generative elements were discovered in the single specimen of this 
coral obtained for examination. 
Stylaster, Gray. 
The genus Stylaster, which gives its name to the family Stylasteridee, was established 
by Gray, in 1831, for the reception of Stylaster roseus, the old Madrepora rosea of 
Pallas, and Oculina rosea of Lamarck, and others. The species, the structure of which is 
here to be described, was obtained off the mouth of the La Plata. It appears to have 
been hitherto undescribed. 
Ceenosteum of Stylaster densicaulis, n. sp. 
‘The ccenosteum (PI. I. figs. 5, @) is flabellate in form, with a very stout main stem 
and branches, which make with one another angles of from 25° to 30°. The main stem 
and larger branches are oval in section, the longer diameter of the ellipse being at right 
angles to the plane of the flabellum. The stem and branches give off numerous 
comparatively small and short ramifying branchlets from their lateral margins. Occa- 
sionally as an exception a branchlet is given off from one of the faces of the flabellum at 
right angles to it, thus distorting its fan-like form. 
° 1 See page 44. 
(ZOOL. CHALL, EXP. —PART v11.—1880.) G8 
