THELACEROS RHIZOPHORA. 557, 
thinner part (/.m. 3) forming the edge of the muscle-mass on 
the side towards the column. ‘This runs vertically down, and 
is inserted in the pedal disc. The longitudinal muscle (/. m. 4) 
nearer the stomodzum than the former is much thicker and 
broader, but has a parallel course. A thin slip of fibres (0. m. 1) 
passes down the mesentery close to its insertion into the column. 
The parieto-basal muscle (/, m. 2) is present, but is not very large. 
I was unable to find any trace of a circular or sphincter 
muscle. And, indeed, contrasting the fully expanded appear- 
ance of the oral disc with the great contraction of the column, 
one hardly expected to find a circular muscle. It seems clear 
that the anemone protects itself by sudden contraction of the 
powerful longitudinal muscles, and that in the fully contracted 
condition the oral disc and tentacles would lie open over the 
rest of the animal. The abnormal form of the tentacles may 
well be correlated with the absence of a sphincter, and there 
may be a certain protective mimicry in the dusky appearance 
of the expanded disc. 
Genital organs were present near the edges of the primary 
and secondary mesenteries ; they were present on the pair of 
directives which I examined. The histological details were 
nearly quite disintegrated, but it was possible to make out the 
remains of ova enclosed in the cavities in the strand of meso- 
gloea. There were no acontia, but the edge of the mesentery 
was thickened, and formed the usual mesenteric filament. I 
give the following tentative definition of the genus. 
Thelaceros (n. g.). 
? With sphincter weak or absent; cesophageal grooves 
weak or absent ; tentacles with compound hollow protuberances 
round the margins of the oral surface; with numerous small 
simple or compound hollow protuberances (rudimentary acces- 
sory tentacles) in radial lines on the oral disc; longitudinal 
muscles exceedingly strong; genitalia on the twelve complete 
mesenteric pairs. 
Thelaceros rhizophore (n. sp.). 
Locality.—Celebes, in a mangrove swamp. 
