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Internal skeleton formed by a coarse network of loose spiculo-fibre,
the subcortical ends of the fibres rising np so as to support the
cortex. A strong cortex composed of a zone of chiefly subhorizontal
skeleton-spicules united by sarcodic substance, and about -45 millim.
in thickness.
Spicules :—(1) Skeleton spinulate, very large, decidedly curved,
tapering gradually to a sharp point; head oval, shaft tapering
slightly towards it, forming a decided but slight neck ; size -8
hy -035 millim. (2) Spinispirular, either delicate, long, composed
of about three bends, which are gradual, so th at no part of the whole
spicule lies much out of the straight line ; size '05 to '056 hy -0016
millim. ; or, rather stouter and shorter, with only two bends, size
•032 by '0022 millim.; in either case ahont 10 sjunes to a bend ;
spines slender, sharp-pointed, -0022 to -0032 millim. long.
Hah. Thursday Island, Torres Straits, 4 -5 fms.
The, unfortunately, single and dry specimen measures 35 millim.
( l i inch) high by 25 millim. (1 inch) in extreme breadth.
The species has in the dry state the colour and much of the
appearance of S. vagahunda ; both forms of spicule, however, are
considerably larger than in th at form and the angulation of the
flesh-spicule is less abrupt. I t is, however, undoubtedly nearly
related to it.
100. Spirastrella decumhens. (P late X L III. fig. c.)
Incrusting, thin (-5 to 10 millim. thick). General surface level
(except where affected by the inequalities of the substance to which
it is attached), glabrous. Colour in spirit grey, slightly tinged
with pink. Vents not made out with certainty. Texture tough
and leathery. Internal structure very compact ; no large spaces
seen, as a rule, in vertical sections. Sarcode dull greenish, subtransparent,
coloured diffusely. Skeletou consisting of loose spicular
tracts, about 6 to 10 spicules broad, running obliquely or at right
angles to the surface, and occasionally forming slight prominences,
protected by the cortex, and of loose skeleton-spicules lying in all
directions between them. Cortex consisting of a layer, two or three
spicules deep, of the flesh-spicule, lying in almost colourless sarcode.
Spicules :—(1) Skeleton spinulate, slender, tapering very gradually
to a sharp point, and very gradually also to the head, below which
the shaft forms a decided and well-defined neck ; head oval, rather
pointed at free end, of about the same diameter as the middle of the
shaft, viz. -0095 millim. ; length of spicule -35 millim. (2) Spinispirular,
moderately stout to stout, consisting of two bends, about
12 spines to a bend ; spines strong, tapering from broad bases to
sharp points, length about -0045 millim. ; length of spicule -025
millim., thickness (excluding spines) -0032 to -0063 millim.
Hah. Alert Island, Torres Straits, 7 fms. (growing over a tubular
Retepora).
This species appears to he more nearly allied in its spiculation to
N. (Alcyonium) purpurea, Lamarck, than to any other Indo-Pacifio
species, hut it differs from it in wanting the magnificent crimson colour
of th at form, in its incrusting habit (purpurea being massive), in
the inferior diameter of the shaft of the spinulate aud the superior
length of the spinispirular spicule (in purpurea these dimensions
are respectively -013 and -016 millim.), the latter usually consisting
in purpurea of only one to one and a half bends.
The single spirit-specimen measures 32 millim. (I^ inch) in
height by 30_ millim. in longest diameter, by 10 millim. ( | inch)
in greatest thickness.
T E T R A C T IN E L L IDA .
The family Lithistidce is not represented. This is not surprising
if it is remembered th a t the depths investigated did not exceed 40
fms.. Mr. Carter’s bettor fortune with collections from Ceylon is in
p art due to the greater depth at which the specimens were obtained.
CHORISTIDÆ.
Sollas, Ann. ^ Mag. N. H. 1882, ix. p. 1.64.
Prof. Sollas has since proposed a different arrangement of the
Tetractinellida, but the division into Choristidæ and Lithistidæ
appears a natural and convenient one. The species obtained,
though few in number, are of remarkable interest, and all new to
the Australian seas.
STELLETTA, Schmidt.
This genus, as at present constituted, is decidedly heterogeneous.
Some of Schmidt’s and Carter’s species appear referable either to
Oeodia, or some genus intermediate between Oeodia and Stelletta
(by virtue of the transitional character of their ball-stellate spicule),
while S. euastrum appears distinct by virtue of its disks. The more
typical forms appear to he divisible into subgroups which coincide
roughly with their geographical distributiou. Thus the Atlantic
species mostly have medium-sized stellates, with numerous rather
coarse, pointed rays ; the Indo-Pacific ones have few-rayed stellates,
usually minute ; of the latter, the Eijian and two of the Ceylon
forms agree in having a small surface bacillate or acerate spicule,
while one Ceylon form (S. tethyopds) and all the Australian ones
known at present agree in having only minute delicate rayed
stellates.
The Indo-Pacific species of Stelletta, s. str., may be divided into
two groups ;—-
Group 1. With baciUar or acerate flesh-spicule.
1. S. (Ecionemia) acervus, Bowerbank, P. Z. S. 1873, p. 322,
pi. X X X . figs. 1-6. Eiji Islands.
2. S. (Ecionemia) densa, id. I. c. p. 322, pi. xxx. figs. 7-14. Eiji
Islands.
3. S. (Tisiphonia) nana. Carter, Ann. & Mag. X. H. 1880 v
p. 138, pi. vii. fig. 43. Gulf of Manaar, Ceylon.
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