Happon—The Actiniaria of Torres Straits. 443 
Habitat—On reefs, Mabuiag and Mer. 
There is a slight difference in the transverse sections of the sphincter of the 
specimens from these two widely separated islands (over 100 miles apart), but I 
do not think it necessary to make distinct species of them. The well circum- 
scribed muscle of the specimen from Mabuiag is shown on Pl. xxvur., fig. 6, 
and that of the specimen from Mer in fig. 7; the latter is about twice the 
size of the former, and both sides of the stem of the muscle are beset with 
mesoglceal plaits. There are numerous perfect mesenteries. 
IXALACTIS* (n. ¢.). 
Bunodidx, with a pedal disk, soft body-wall, which is smooth below and 
verrucate above; tentacles very numerous, with alternately large and small 
transverse swellings on their oral surface; the tentacles are mainly disposed 
round the periphery of the oral disk, but some occur on the central zone of 
the disk; sphincter muscle circumscribed, endodermal. 
Ixalactis simplex (H. & S.). 
Phymanthus simplex, Hadd. and Shackl., 1898, Proc. R.D.S. vur, p. 123. 
(Pl. XXV., figs. 15-19; Pl. XXVIIL., figs. 8, 9.) 
Column.—Soft, corrugated when contracted; lower portion smooth; upper 
portion with suckers, which are larger below, smaller above; parapet crenu- 
lated, the crenulations agreeing with the mesenterial chambers. 
Disk.—F lat, when fully expanded, often thrown into half-a-dozen folds, never 
completely retractile (Pl. xxv., fig. 15). Mouth rounded; stomatodeeum, with 
two cesophageal grooves, which are not very distinct. 
Tentacles.— Of two kinds, centripetal and centrifugal :—(1) The inner tentacles 
are arranged in three cycles, and extend from about one-half to one-third of the 
radius of the disk, starting from the mouth; the inner cycles are about 48 
in number. (2) The marginal tentacles are arranged in four or five cycles, and 
consist of probably about 192 tentacles (6 + 6 + 12 + 24 + 48 + 96 = 192). 
Aboral aspect of each tentacle rounded, smooth; oral aspect, flattened with 
symmetrical lateral swellings, which are alternately large and small, the former 
being some half dozen in number (PI. xxv., figs. 17-19). The inner tentacles 
are slightly the larger. Tentacles irritable and contractile; when contracted 
*T have named this genus from the resemblance that the side view of a tentacle (PI. rv., fig. 17) has 
to the horn of an Ibex, té%Aos: epithet of the Ibex; of. Iliad iy. 105: igddov atyos dypiov. 
38T2 
