94 
THE VOYAGE OF H.M.S. CHALLENGER. 
it is probably not much over 0*06 mm. Protocladus 0'052 by 0'021 mm.; deutero- 
cladus 0'036 mm. long; tritocladus 0'0276 mm. long; tetracladus 0‘0276 mm. long. 
The dichotomy of the cladus is not confined to a single plane. 
II. Microscleres. 3. Microxea, smooth, more or less fusiform; 0T18 by 0'004 mm. 
4. Microxea, trichose, covered with minute, erect spines; 0’0276 mm. long. 
5. Spir aster, spines of hair-like fineness ; 0'0118 mm. long. 
Habitat . — Station 192, September 26, 1874; lat. 5° 49' 15" S., long. 132° 14'15"E. ; 
depth, 140 fathoms ; bottom, blue mud. 
Remarks. — The mesotrisenes of this sponge occur isolated in the insoluble residue left 
after treating with hydrochloric acid a fragment of limestone on which a species of 
Lithistid is seated. For further information regarding this sponge I am indebted to the 
kindness of Mr. Carter, who presented me with two slides, labelled Samus quadripartita, 
and bearing mounted fragments of sponge tissue containing the characteristic mesotrisenes 
of Triptolemus and the associated microscleres. The spined microxeas form a loose felt 
similar to that of Pcccillastra, the mesotrisenes lie with the cladi on the whole parallel to 
the surface of the sponge, and the actines directed at right angles to it. Other spicules 
occur with those of Triptolemus, notably a curious rhabdus or style, bent at the blunt 
end at right angles like a trenail ; this belongs to a sponge named by Carter Microciona 
intexta, var. This is interesting, because a precisely similar spicule occurs along with 
the mesotrisenes of my slides, and it would hence appear probable that Carter’s specimens, 
the habitat of which is unknown, were obtained from near the same locality as those 
brought home by the Challenger. The dimensions given for the mesotrisene are taken 
from the largest spicule I could find ; in other instances difierent measurements were 
obtained, the deuterocladus being sometimes longer than the protocladus — in one instance it 
measured 0’055 mm., aiid the latter only 0‘035 mm. The dichotomy is not always repeated 
four times ; in many instances the spicule is only tricladose, and it frequently happens 
that two cladi may be tricladose and the third tetracacladose only on one side, i.e., 
tetracladi only appear at the ends of two of the tritocladi arising from the same deutero- 
cladus, the tritocladi of the other deuterocladus not branching further. 
