10 
THE VOYAGE OE- H.M.S. CHALLENGER. 
terminate within the spicule without affecting its form, are wholly and highly porrectate, 
reminding one of the two shorter cladi which occur in protrisenes characterised by one 
cladus much longer than the other two. 
Tetilla grandis, Sollas (PI. V. figs. 1-14). 
Tetilla grandis, Sollas, Prelim. Account, Sci. Proc. Roy. Dubl. Soc., vol. i. [j. 180, 1886. 
Sponge (PI. V. figs. 1-3) large, somewhat cylindrical or ellipsoidal in form, anchor- 
ing filaments matted together to form a massive base. Oscules several, comparatively 
small, the patent openings of the excurrent canals, chiefly distributed on the summit 
of the sponge. Surface more or less hispid, raised into ridges and low’- papillae, which 
unite to form an irregular reticulation, in the depressions of which the pores are 
situated in groups. Ectosome thicker than in most Tetillse, consisting of fibrous and 
fibro-vesicular collenchyma. The skeleton consists of spicular fibres radiating spirally 
from an excentrically situated core. 
Spicules. — I. Megascleres. 1. Oxea, fusiform, anisoactinate, the distal end more 
obtusely pointed than the proximal, which is sometimes almost filiform. The difference 
between the two ends is less marked in spicules occurring near the origin of the fibre, 
than in those which form its peripheral ends, where they may sometimes be seen with 
the distal end quite rounded off, or strongylate ; from 6'07 by 0‘075 to 5 '72 by 
0'079 mm. 
2. Protrisene, rhabdome cylindro-conical, diminishing from the cladome to a fili- 
form termination ; cladi typically three in number, but frequently reduced to two or even 
one. Ehabdome 8 ‘6 by 0.0158, cladi 0‘15 by 0’0118 mm. 
3. Trichodal protrisene, usually with one cladus longer than the other two, ’which are 
equal in length ; chiefly disposed about the cribriform areas over the incurrent canals. 
4. Somal anatrisene (PI. VI. fig. 6) a fusiform rhabdome, attenuated proximally 
to a filiform extremity, distally at first diminishing and then increasing in diameter 
up to the cladome ; cladome rounded in front, axial fibre not prolonged into it, cladi 
long, slender, springing from the rhabdome in a bold sweeping curve. Ehabdome 12T4 
by 0'02 mm. just below the cladome, diminishing to 0'006, and then increasing to 0*0118 
mm. in diameter, finally tapering to its filiform extremity; cladi 0*158 by 0*0118, chord 
0*16 mm. 
5. Radical anatrisene. The cladal end of the rhabdome is much thicker than that 
of the cortex, and provided with shorter stouter cladi ; the axial fibre of the rhabdome 
extends halfway into it. The rhabdome is thickest just below the cladi, and somewhat 
rapidly tapers for the first half of its course, and then more gradually till it ends in a 
filiform termination. Ehabdome 31*5 by 0*0315 near the origin of the ’cladi, 0*0276 
just beyond their points, and 0*021 mm. a little more than a millimeter lower down; 
