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7 9 . RhaphidopMus arborescens. ( P l a t e XL. fig . L ;
P l a t e X L II. f ig s . n, n'.)
Sponge stipitate, much branched, bnsh-like ; branches angular
rather than cylindrical ; surface nodular, connected by frequent
■ ■ ■ ■ - -
horizontal trabeeulæ at right angles to the erect branches.
average diameter of the stem aud its branches is 4-5 millim.
The
cortical incrustation of spicules consists of a layer about '5 millim.
thick, the outer part of which consists of loose fascicles of the
smooth spinulate spicule, with the pointed ends placed outermost ;
the spicules are closely approximated to each other below the
surface, between the intermarginal canals, but their distal ends
diverge and spread out somewhat at the surface, and between
them appear to he placed the pores ; the intermarginal canals,
as stated, lie between the bases of these fascicles. The deeper
part of this layer consists of Halichondrioid spiculo-fibre, about 6-8
spicules broad, with small roundish or polygonal meshes, which seem
to have enclosed small canals (probably the aflferent canals loading
from the intermarginal cavities to the ciliated chambers). Xo
horny matter is to bo seen in this part of the skeleton, the extreme
fragility of which forbids the idea th at any such occurs here [on
the contrary, tho compressibility aud readiness with which the
spicules and fibres must he able to move upon each other in life,
owing to the manner of their aggregation, point to a probable great
power of contractility and expansion in the dermal membrane, with
important consequences to the pores, intermarginal cavities, and
inhalent canals which it contains ; and I should anticipate th at good
spirit-specimens would show the strong development here of muscle-
cells, such as has been shown hy Prof. Sollas in Tetilla (Ann. &
Mag. X. H. 1882, ix. p. 155)]. The fibres of the skeleton are irregular
; their course is winding, and the distinction between primary
and secondary fibres not clear, except at the surface ; here the ends
of the primary fibres, which stand out for some distance beyond the
general reticulum and support the dermal crust, are absolutely concealed
by the enormous abundance of points of the spined spicules
which project from them.
Spicules :—(1) Slightly spinulate, smooth acuate, -34 by -0063 ;
(2) Spined acuate, slightly constricted hasally, -08 hy -0044 ;
(3) Delicate equianchorate, palms proximally square, -012 millim.
long.
Hab. Friday Island, Torres Straits.
The specimen, which is dry, measures 125 millim. (5 inches) in
height and 60 miUim. (2|- inches) in maximum diameter.
Vosmaer’s Clathria ulmvs (Notes Roy. Mus. Netherl. ii. p. 151)
resembles this species, but is stated to have a bihamate flesh-
spicule, and no dermal crust is described. The species differs from
R. cratitius, Esper, in the well-branched habit and in minor points in
the proportions of the spicule. Ehlers (Espersch. Spong.) assigns
a bihamate to that species *. assigns
80. Rhaphidophlus procerus. ( P l a t e XX XIX fig K •
P l a t e X L II. figs. o-o".) ' ’
Erect, cylindrical, or very slightly compressed. Stem tapering to
a point above, commencing with a cylindrical approximately smooth
f h i r it gradually increases in
diameter towards the middle, where the antero-posterior diameter
IS 7, the lateral diameter 8 millim.; the lateral surfaces show a
tendeucy to develop a succession of low upwardly-projecting eminences
; the anterior and posterior surfaces of this (middle) division
ot the sponge are covered with closely-set rounded papillæ, 1-2
millim. apart, 1 milhm. broad hy -5 to 1 millim. high; the upper
ourth tapers gradually to the apex and is approximately smooth,
toe papillæ of the median part becoming gradually obsolete here.
No true branches (only two small cylindrical processes on one
E l r f B a s e formed by several
branched roots, 3 to 5 milhm. in diameter. Surface smooth between
and over eminences, compact, soft and velvet-like to the touch • no
vents visible to the naked eye. Texture in spirit firm, very slightly
compressible, flexible, very tough ; colour pale grey. ° ^
Mam skeleton consisting of a close network of amber-coloured
horny or dull subopaque yellow horny sarcodic fibre, the primary
mes of which cto about -2 millim. apart and are placed vertically
to the surface the secondaries also about -2 millim apart, crossing
Î between the primaries at approximately right angles ;
to the fibres are attached by their bases large numbers of the larger
smooth spinulate spicule, whose points project outwards and upwards
æt acute angles to the fibre. Dermal skeleton formed of a single
thickness of distinct, but overlapping, dense tufts of the smaller
smooth spinulate spicule, one or more of the spined acuate spicules
occupying the centre of each tu ft; the spicules are attached by
then hlunt e n d / and the points radiate outwards over the dermis
barcode pale yellowish brown, somewhat granular.
Spicules ( I) _ Smooth spinulate ; head distinct, suhoval, rather
narrower than I middle -l-v-»-I <-11 y, of s ~ 1_______h a ft; shaft 1 Ol tapering I • gradually ^ to ' sharp
point from about middle; size -36 by -0127 millim: in fibre of
mam skeleton. (2) As (I), but measuring-28 by -0079 millim •
forming tufts m dermis. (3) Spined acuate, with well-rounded, u l -
dilated base, tapering to sharp point from base ; spines usually
absent from_ the apex and ju st above base, stout, sharp, those of
median portion of spicule more or less recúrvate towards base; size
i i by -012/: m centre of dermal tufts and sparingly in main-skeleton
* fo n g ia cactiformis, Lamarck (Ann. Mus. Hist. Nat. xx. p. 440), is also a
fosH t . l ? ’ uiuoresceiis,arhoreseens, so so lar far as a s the th e m materj
a te ria l at m y disp
o s a l m a in ly in th e SDinulation n f fViA «mrwrfV»
posal shows, mainly in the non-spinulation of the smooth acuate. :