Happon anp DurrpEN—Some Actiniaria from Australia and other Districts. 147 
The endoderm is very uniform and thin, and crowded with zooxanthellae. A 
weak diffuse endodermal muscle can be distinguished. 
Sphincter muscle——The single mesoglceal sphincter muscle extends for a 
considerable distance. 
Dise and Tentacles.—TVhe ectoderm of the dise is rather thick, crowded with 
zooxanthelle and pigment particles, and that of the tentacles is crowded with long 
narrow nematocysts; the mesogleea is thin, with incrustations and cell-islets ; the 
endoderm is thin and crowded with zooxanthelle. 
@sophagus.—The ectoderm of the cesophagus is folded, a well-marked groove 
occurs ; large yellow oval nematocysts and narrow elongated ones are abundant. 
The mesoglcea is thin, but thickens a little at the cesophageal groove ; it does not 
follow the foldings of the ectoderm ; cell-islets occur in it. 
Mesenteries.—These show the brachycnemic character well. The reflected 
ectoderm is well developed; below the cesophagus the mesenterial filaments or 
craspeda are large, and, like the ectoderm of the cesophagus, are crowded with 
the two kinds of nematocysts. The mesogloea is very thin, except where it is 
perforated by the large basal canal; this contains large nematocysts. Smaller 
canals or sinuses also occur in the mesoglea. The endoderm has numerous 
zooxanthellze, and slight parieto-basilar muscles occur, and a very slight retractor 
muscle. 
Gonads.—-None present in any of the polyps examined. 
It is extremely difficult to define the species of this genus, as we do not yet 
know what variations may take place in a given species owing to difference of 
environment. 
Turning to the forms from the Indian Ocean, we have P. tuberculosa (Esper) 
fide Klunz., 1877; P. flavo-viridis and P. argus, Ehr., 1834, all from the Red Sea. 
Klunzinger states the two latter are synonyms of the species which he describes 
and which he allocates to Esper’s Aleyoniwm tuberculosum. Esper (Der Pflanzen- 
thiere, m1. Alcyonium, p. 68) gave the name of Alcyonium tuberculosum to a 
Palythoa, from ‘‘'Trankenbar” (probably Trankuebar, lat. 11° N., on the east 
coast of India), which he thought was the same as the A. papillosum of Pallas, 
from an unknown locality. His figure (Pl. xxm., fig. 1) of the upper surface 
of the colony is not satisfactory, and does not agree with his description 
of the polyps growing thickly together, forming wart-like elevations of unequal 
$1Ze. 
Hertwig investigated a specimen collected by the “ Challenger,’ at Simon’s 
Bay, Cape of Good Hope, and this he identified with Klunzinger’s form. We 
speak with all caution and deference, but we venture for the present to uphold 
the doubt cast by one of us on this identification (Trans. R.D.S., 1891, p. 631). 
The very close opposition of the polyps, resulting in the markedly polygonal 
TRANS. ROY. DUB. SOC., N.S., VOL. VI., PART VI. QA 
