SPONGES FROM THE ABEOLHOS ISLANDS. 50? 
all the known Anstraliaii specimens of Tracliycladus, as well as Lendenf eld's 
Spirophora digitata and Spiropliora bacterium, should be included iu Traehi/- 
cladus lavispirulifer Carter. 
Previously hioion Distrihution. South-West Australia [Carter') ; Port 
Phillip Heads, Australia {JJendy). 
Register No. and Locality. III. it, Wooded Isle. 
40. SiGMOSCEPTRELLA FIBROSA IJeildy . (PI. 25. fig. 14.) 
Spirastrella fibrosa Dendy [1897]. 
Sigmosceptrella fbrosa I)eudy [1921 A]. 
The single fine specimen in the collection, which measures 70 mm. in 
height, is sessile and lobodigitate. Surface sub-glabrous, almost smooth in 
parts, slightly conulose or nodular in others. The close-set inhalant pore-areas 
give the surface a minutely reticulate sippearance. They overlie large, funnel- 
shaped chones in the cortex, which is slightly fibrous and measures up to 
0"4 mm. in thickness. The roof of each chone is not merely a dermal membrane, 
but is moderately thick, strengthened by microscleres (sigmodiscorhabds), 
and pierced by individual pores which take the form of short canals. The lower 
part of the chone is constricted to a relatively small opening, which leads 
into a spacious subcortical crypt ; from this, inhalant canals, provided with 
diaphragms along their lengtii, penetrate the choanosome. The canal system 
is eurypylous, the flagellate chambers spherical and measuring up to 0"05 mm. 
in diameter. The larger exhalaiit canals and the wide oscular tubes are sur- 
rounded by a thick layer of gelatinous mesogloea. Vents small but 
prominent, scattered singly on the upper margin of the sponge, sometimes at 
the ends of small conical projections. Each vent is much smaller than the 
diameter of the oscular tube out of which it opens, so that the latter appears 
to have a thin roof with the vent in the middle. Colour in spirit yellowish 
white; texture firm, compact, resilient. 
The skeleton arrangement agrees closely with Dendy's original description. 
Between the chones the cortex is packed with microscleres, intermingled in 
places with the ends of the radial bundles of megascleres. 
Spicules : — (1) Styli ; straight, evenly rounded or slightly enlarged at the 
base and sharply pointed at the apex, very uniform in shape and size, 
measuring about 0'34 by O'Ol mm. 
(2) Isodiscorhabds (sigmodiscorhabds) ; measuring in total length about 
O'Oo mm.; the diameter of the smooth shaft is about 0"008 mm., that of a 
whorl with the spines included 0'025 mm. The development and adult form 
of these spicules have been described and figured by Dendy in "The 
Tetraxonid Sponge Spicule — A Study in Evolution" [L921 A]. 
Previously knoivn Distribution. Port Phillip Heads {Dendy). 
Register No. and Locality. VI. 2, Sandy Isle. 
