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



transparent, parchment-like dermal membrane, covering the large subdermal cavities, 

 and constituting a very characteristic feature of the species (PI. XXVIII. fig. 3a). 

 Oscula smaU and scattered (?) (there are a great number of round openings in the 

 dermal membrane, especially on one side of the sponge, which might readily pass for 

 oscula, but it is impossible to say how far they are due to shrinking back of the dermal 

 membrane from the action of the spirit). Pores ; on one side of the sponge are a number 

 of small oval areas in which the dermal membrane is rediiced to a sieve by numerous small 

 perforations, which are the pores. The pore-areas are well defined and rather sparsely 

 scattered ; it is curious that they should occur on ,one side only, that being the side on 

 which most of the oscula (?) are situated. Diameter of pore-areas and pores variable, of 

 the former averaging about 0'5 mm. of the latter about 0"! mm. 



Skslet07i.— In balsam preparations the arrangement of the skeleton somewhat 

 resembles that of Plumohalichondria, the chief feature being a series of ascending, 

 plumose columns, each consisting of a core of very slender, subtylostylote spicules 

 echinated by entirely spined styli, the horny matter being almost invisible ; but on 

 examination in alcohol we see that there is a very large proportion of pale homy substance 

 in the skeleton, which is arranged as follows : — There is a well-defined reticulation of 

 horny fibre ; branching primary fibres run upwards in wavy lines, ending at the surface 

 of the sponge, and these alone are cored by long, slender, subtylostylote spicules. 

 Secondary fibres cross the primary lines without much regularity, forming an anastomosing 

 reticulation, and both series of fibres are echinated by spined styli. In the dermal 

 membrane there are numerous subtylostylote spicules, scattered and in brushes. 



S2ncides. — (a) Megasclera; of two kinds. (1) Very slender, straight, smooth sub- 

 tylostyli (PI. XXIX. fig. 14), measuring about 0"2 by 0'003 mm.; (2) straight, slender, 

 sharp pointed, entirely spined, echinating styli (PI. XXIX. fig. 14a), measuring about 0'07 

 by 0'0032 mm. (b) Microsclera; of one kind only, viz., palmate isoehelee (PI. XXIX. 

 fig. lib), of rather unusual form, with very slender shaft, rather strongly curved and 

 making an unusually wide angle with the front palm ; length about 0"02 mm. 



This sponge is most readily recognised by its beautiful and characteristic external form. 



XocaZ%.— Station 162, April 2, 1874 ; lat. 39° 10' 30" S., long. 146° 37' 0" E. ; ofi" 

 Moncoeur Island, Bass Strait; depth, 38 fathoms; bottom, sand and shells. One fine 

 specimen. 



Clathria inanchorata, Ridley and Dendy (PI. XXVIII. fig. 4; PI. XXIX. 

 figs. 13, 13a). 



1886. Clathria inanchoraia, Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 5, vol. xviii. 



p. 475. 



Sponge (PI. XXVIII. fig. 4) erect, slender, of very peculiar, rugged external 

 appearance, the best idea of which wiU be obtained by reference to the figure. The 



