24 
THE VOYAGE OF H.M.S. CHALLENGEK. 
rare on the summit, chiefly distributed in an irregular zone round the sides of the body. 
Surface hirsute, with obliquely projecting spicules ; projecting ends longer over the sides 
than the summit of the sponge. 
Spicules. — I. Megascleres. 1. Somal oxea. large (PI. III. fig. 4), fusiform, sharply 
pointed, straight, or curved in correspondence with the curvature of the spicular fibres, 
8-03 by 0-071 mm. 
2. Cortical oxea (PI. III. fig. 7) smaller than the preceding, cylindrical or fusiform, 
usually curved, obtusely pointed, 0*892 by 0-0355 mm. 
3. Protrisene (PI. III. fig. 6). A somewhat fusiform rhabdome, 0*0197 mm. wide just 
below the cladome, increasing to 0*0296 where widest, and then tapering to a filiform 
extremity; its length is 13*21 mm. The cladi, usually three in number, but sometimes 
reduced to two or even one, are conical, 0*1776 mm. long, and 0*016 mm. broad at the base. 
4. TricTiodal protrisene. A slender filiform rhabdome, and three cladi usually 
unequal in length. Dimensions : — Ehabdome 0*13 by 0*0039 mm. ; cladi very variable, 
two shorter and unequal 0*016 mm. long, one longer from 0*0237 to 0*031 mm. long. 
5. Anatrisene (PI. III. fig. 5). Confined to the lower part of the sponge-body ; the 
rhabdome long, somewhat fusiform but nearly cylindrical, terminating at the proximal 
end in a filiform extremity ; cladome variable in shape, axial fibre of shaft prolonged 
into it ; cladi usually much recurved, sometimes so much so as to become parallel with 
the rhabdome. Dimensions : — An anatrisene with its cladome embedded in the cortex 
gave the following measurements: — Ehabdome 19*6 by 0*0316 mm.; cladi 0*215 by 
0*0276 mm., chord 0*2 mm.; length of cladal end of the rhabdome 0*059, extension of 
axial fibre into it 0*0119 mm. An example from the anchoring filaments of the base 
gave : — Ehabdome 40 mm. by 0*0237 just below the cladome, lower down 0*0158 mm. 
in diameter, from this increasing to 0*0235, and finally attenuating to a filiform 
extremity; cladi 0*087 by 0*0197 mm., chord 0*09 mm., length of the cladal end of the 
rhabdome 0*0474 mm. The cladome of this specimen is smaller than the average, a more 
usual size for the cladi is 0*1026 by 0*0158 mm., chord 0*118 mm. 
II. Microscleres. 6. Sigmaspire (PI. III. fig. 8) of the usual form, 0*0118 to 0*0156 
mm. long. 
7. Globules; accessory or accidental forms, 0*0535 mm. in diameter. 
Colour. — Ashen-grey. 
Habitat. — 'Station 149b, off Eoyal Sound, Kerguelen, January 17, 1874; lat. 49° 28' 
S., long. 70° 30' E.; depth, 25 fathoms; bottom, volcanic mud. 
Station 149c, Balfour Bay, Kerguelen, January 19, 1874; lat. 49° 32' S., long. 
70° 0' E.; depth, 60 fathoms ; bottom, volcanic mud. 
Remarks. — Over sixty specimens of this remarkable sponge, the only species 
of the genus, were dredged off the shores of Kerguelen. They vary considerably 
