REPORT ON CORALS— HYDROCORALLIN^E. 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. 1 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 Stylasteridse 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 (PI. V. D D). 



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 

 ccenosarcal mesh work, 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 Stylasteridse, 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. 



Ccenosteum of Stylaster densicaulis, n. sp. 



The ccenosteum (PI. I. figs. 5, a) 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 branchlcts 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 VII. — 1880.) G 8 



