404 Happon—The Actiniaria of Torres Straits. 
Commensal on a worm tube (said by Saville-Kent to be a species of 
Nereis; but it may be a species of Eunice. Cf. F. Buchanan, “Note on the 
Worm associated with Lophohelia prolifera,” Proc. R. D. S. (N. 8.), vit, 1897, 
p- 432). 
Found at low tide round the shores of tropical Australia. 
The chief point of interest about this species is the habit it has of asso- 
ciation with a tubicolous Annelid. It is evident that the growth of the 
Zoanthus annoys the worm, owing to its tendency to grow over the terminal 
orifice. In order to escape, the worm makes a fresh start in another direction, 
but usually in the same plane, and at a divergent angle of about 60°. 
Before it has added another inch to its dwelling tube, the polyp has once 
more overtaken it, and converted its front entrance into a cul-de-sac. This 
process is repeated again and again with great regularity. After about a 
score or so of obliquely ascending short branches, the polyp appears to be 
victorious in this zigzag race; for one generally finds that about this stage 
the tube is uninhabited, and the polyps sit on the closed apertures of the 
lateral and terminal branches. 
Mr. Saville-Kent, when he first described this species, considered that the 
Zoanthean secreted the tube. In a previous correspondence I argued against 
this view, and subsequently I wrote a short Paper, in which I pointed out 
that branched worm-tubes were by no means unknown, although Mr. Saville- 
Kent had overlooked the fact. I there stated that, anatomically, the 
Zoanthean belonged to the genus Zoanthus; but that it was a new species. 
In his recently published book, Mr. Saville-Kent records the discovery of 
the worm which secretes the tube; and so that point is now settled. He 
still retains his own generic name for the polyp; but I have no doubt that 
it must lapse. 
The anatomical characters of this species do not call for any special remark. 
The ectoderm cells are found as in Z. Jukesii and Z. Coppingeri; the cuticle is very 
feebly developed. The ectodermal canals in the mesoglea are numerous and ~ 
large, and have a tendency to form a disconnected ring near the endoderm. The 
distal portion of the double sphincter muscle is much more powerful than the 
proximal, which alone serves to distinguish it from other Zoanthez of Torres 
Straits. 
ISAURUS, Gray, 1828. 
Large brachyenemic Zoanthex, with a single mesogleal sphincter muscle. The 
body-wali is unincrusted; the ectoderm discontinuous; ectodermal and endo- 
dermal bays and small canals in the mesoglea. Moncecious or dicecious. Polyps 
in small clusters or solitary. 
