4 
THE VOYAGE OF H.M.S. CHALLENGER. 
longer cladus 0'197 mm,, the shorter 0’1065 mm. long. In another specimen this spicule 
is 6 ’426 mm. long. 
4. Trichodal protrisenes (PL I. figs. 10, 11, 12). Similar in general form to the 
preceding, hut much smaller and remarkably tenuous, so as to appear hair-like. The 
unpaired cladus much longer than the paired cladi. Ehabdome 1‘162 mm. long; unpaired 
cladus 0'06 mm., paired cladi 0’012 mm. long. 
5. Somal anatrisene (PI. I. figs. 4, 7). Ehabdome fusiform, expanding at the cladal 
origin, cladi fong and slender, cladome rounded off in a wide curve in front, axial fibre of 
the rhabdome not produced beyond the origin of the cladi. Ehabdome O'Ol mm. in 
diameter in the middle, tapering to a filamentous proximal end, distally at first attenu- 
ating to a diameter of 0'004 mm,, then growing thicker till it attains a diameter of 
0'0158 mm. immediately below the cladome; length about 6'0 mm.; cladi 0‘118 by 
0'012 mm. In another specimen the dimensions of the spicule are as follows : — Ehabdome 
7*4 by 0’0197 mm. below the cladome, diminishing to 0*004, increasing to 0*0078 mm,, 
and then attenuating to the proximal extremity; cladi 0*079 by 0*0118 mm., chord 
0*142 mm. 
6. Radical anatrisene (PI. I. fig, 6). This is distinguished from the somal anatrisene 
by the characters of the cladome, which is more massive, and terminates distally in a 
rounded mucrone ; the axial fibre of the rhabdome is continued forwards past the origin 
of the cladi to the end of the mucrone. Ehabdome from about 6*05 by 0*0355 mm. to 
6*79 by 0*0276 mm., cladi 0*154 by 0*0237 mm., distal extension of axial fibre 0*0276 mm. 
In another specimen this spicule has the following dimensions ; — Ehabdome 7 *5 by 
0*0276 mm. below the cladome, diminishing to 0*0118, and then increasing to 0*0158 mm.; 
cladi 0*122 by 0*0197 mm,, chord 0*118 mm., axis of rhabdome continued past the origin 
of the cladi for 0*0197 mm. 
II, Microsclere. 7. Sigmaspire (PI. I. fig. 8). Of the usual form, from 0*0138 to 
0*0197 mm. long. 
Colour. — Ashen-grey. 
Habitat. — Station 320, off the Eio de la Plata, South America, February 14, 1876; 
lat. 37° 17' S., long. 53° 52' W. ; depth, 600 fathoms; bottom, green sand; bottom tem- 
perature, 37° *2. 
Remarhs. — Six specimens of this sponge were trawled. AU are more or less spherical, 
except one which is a prolate ellipsoid. The specimen figured measures 15 mm. in 
height, or 30 mm. if the anchoring filaments be included, and 17 mm. in breadth ; the 
smallest specimen is 5 mm. high by 4 mm, broad. 
The single oval oscule is excentrically placed on the obliquely depressed upper 
surface of the specimen figured. It measures 3*18 by 1*6 mm. Its margins are pro- 
duced into a short membranous tube, strengthened by a dense layer of longitudinally 
