80 
THE VOYAGE OF H.M.S. CHALLENGER. 
cortex where it surrounds the poriferous area. It already presents, at the entrance to the 
poriferous area, cells remarkably like sense-cells (PI. XXXIX. figs. 6, 7). In the next 
smallest specimen (PI. III. fig. 9), over 4 mm. in diameter, the walls of the cloacal 
chamber are thicker, more deeply invaginated, and the whole structure is essentially 
similar to that of the adult oscule and chamber. The spiral arrangement of the 
spicular fibres is already well developed in the youngest specimen, and the young oxeas 
are bent in exact accordance with the curvature of the spiral, which is not much more 
than one spicule in length ; thus showing that the spiral is not due to the form of the 
spicules, but the form of the spicules to the spiral ; both are caused by a spiral growth 
of the sponge. 
Craniella, 0. Schmidt. 
The cortex is differentiated into an inner fibrous layer traversed radiately by cortical 
oxeate spicules, and an outer collenchymatous layer, excavated by subdermal cavities. 
The choanosomal mesoderm is a sarcenchyma ; the chamber system aphodal. 
Craniella simillima (Bowerbank) (PI. II. figs. 5-20 ; PI. IV. figs. 23-31). , 
Tethea simillima, Bwk., pars, Proc. Zool. Soc. Lond., p. 15, pi. iii. figs. 7-8, 1873 (South Seas). 
Craniella Bowerhankii, Sollas, Prelim. Account, Sci. Proc. Roy. Dubl. Soc., vol. v. p. 181, 1886. 
Sponge subspherical, surface conulose ; a single oscule at the summit, its position 
indicated by the greater length of the conules which project around it; base distinguished 
by a general pilosity and absence of conules. 
Spicules. — I. Megascleres. 1. Somal oxea, anisoactinate (PL II. fig. 6 ; PI. IV. 
fig. 24), fusiform, maximum diameter nearest the distal end ; proximal end highly attenu- 
ated; 3'26 by 0'047 mm. 
2. Cortical oxea (PL IV. fig. 27), fusiform, 1‘4 by 0‘04 mm. 
3. Protrisene (PL II. figs. 7, 8, 14, 15 ; PL IV. figs. 26, 28). Rhabdome slightly 
narrower just below the cladome than a little further down, attenuated to a filiform 
distal end; rhabdome 5T2 by 0’02 to 0*024 mm.; cladi 0*12 mm. long, chord 0*06 
to 0*07 mm. 
4. Anatrisene (PL II. figs. 9, 10, 16, 17 ; PL IV. figs. 25, 29). Rhabdome at first 
nearly cylindrical, thin, tapering to a filiform extremity ; cladome almost conical, 
somewhat pointed in front; axial fibre of rhabdome continued into it 0*016 mm. past 
the origin of the cladal axes; cladi conical, rather short; rhabdome 5*8 by 0*02 mm.; 
cladi 0*058 mm. long, chord 0*08 mm. 
II. Microscleres absent. 
