72 THE VOYAGE OF H.M.S. CHALLENGER. 



the thickness and the length varying from 1 : 10 to 1 : 12. In the spaces between the 

 osoula these triradiate spicules lie pretty regularly, their corresponding rays being 

 dispose! more or less parallel one to auother, their basal ray turned to the closed end of 

 the Sponge, and the angle between the lateral rays towards the sharp margin dividing the 

 sieve-like surface from that bearing oscula. Near these latter, as well as near the margin 

 just mentioned, their disposition becomes irregular, they lose their characteristic shape, 

 presenting all possible transition-forms to the sagittal triradiate spicules of the sieve- 

 like surface, and, on the other hand, growing smaller, to the rectangular triradiate ones of 

 the oscular skeleton. 



Large (ten-ate spicules of the convex surface. — Lying in several layers almost parallel to the 

 surface, causing its smoothness and silvery lustre. Form, length, and comparative thickness 

 extremely variable, either spindle-, club-, or lance-shaped, or of quite irregular outline, 

 reaching 1 mm. in length (usually shorter), the proportion between their length and 

 thickness varying from 8 : 1 to 30 : 1. 



Oscular acerate spicules. — Spindle- or lance-shaped, usually twenty-eight times as loug as thick, 

 rarely longer than 055 mm., often considerably shorter. 



Oscular triradiate spicules. — Sagittal, basal ray forming with each of lateral rays an angle of 90"; 

 basal ray straight, tapering from the base to a sharp point, usually half as thick as lateral 

 rays, often still thinner, occasionally almost of the same diameter; length inconstant, 

 rarely longer than 0'05 mm., often not exceeding O'Ol mm. or still shorter ; lateral rays 

 either straight, or slightly curved inwards, usually sharply pointed, ten times as long as 

 thick, average length 01 mm. ; connected as regards their form and size with the sagittal 

 subdermal triradiate spicules of the oscular surface by a long series of intermediate stages. 



Oscular ouaclriradiatc spicules. — Like the rectangular triradiate, nothing but modified sagittal 

 triradiate spicules of the oscular surface ; lateral rays either straight or slightly curved 

 forwards, tapering from the base to approximately sharp points, average length 0'2 mm. by 

 002 mm., basal ray usually rather shorter, straight, sharp-pointed, forming with each of 

 lateral rays an angle of about 110° ; apical ray curved, not seldom undulating, sharp-pointed 

 like the facial rays, usually rather thinner than these latter ; length varying from - 06 to- 

 0'2 mm. 



Colour.— White. 



Habitat. — Station 163a, June 3, 1874, off Port Jackson; depth, 30 to 35 fathoms; 

 rock. Station 1G3, April 4, 1874 ; lat. 36° 56' S.,long. 150° 30' E.; depth, 120 fathoms ; 

 off Twofold Bay, Australia. 



In order to render conspicuous the comparative richness of the Challenger Stations in 

 Calcarea, I give here the following Table, showing also the depths from which the Sponges 



were dredged. 



