Sponge-fauna of Norway. 133 



spicules may be divided into two groups, the robust and the 

 slender. 



Thick long-shafted Spicules. — (i) a simple fusiform, straight 

 or slightly curved, sharply pointed acerate, 0*235 inch long, 

 0-0025 inch broad (PL VI. fig. 4) ; (ii) trifid spicule with 

 simple rays, shaft 0*16 inch long, 0*0025 broad, arms 0'03 

 inch long (PL VI. fig. 5) ; (iii) trifid spicule with bifurcated 

 arms, shaft 0*11 inch long, 0*00375 broad, arms 0*0375 inch 

 long (PL VI. figs. 6, 8). 



Thin long-shafted Spicules. — (i) a long, slender, sharp- 

 pointed acerate, 0'23 inch long (PL VI. fig. 11) ; (ii) trifid 

 spicule with forward-directed arms, 0*215 inch long (PL VI. 

 fig. 10); (iii) trifid, with arms recurved, anchor-like, 0*216 inch 

 long (PL VI. figs. 9, 15) ; (iv) trifid spicule with forward- 

 directed arms, 0*0625 inch long (PL VI. fig. 7). All these 

 spicules are about 0*00125 inch broad. No. iv is no. iii of 

 the preceding group in miniature. 



Stellates. — These are of two kinds : — one somewhat larger, 

 0*0013 inch in diameter, with fine pointed rays (PL VI. 

 fig. 13) ; the other smaller, 0*0004 inch in diameter, with 

 blunt-ended rays and less regular in form (PL VI. fig. 12). 

 Bowerbank's term " cylindro-stellate " may be adopted for 

 the latter. 



Hair-like Spicules or Trichites. — The " trichites," as these 

 fine, immeasurably thin, hair-like spicules may be termed, are 

 usually collected together in cylindrical sheaves or bundles, 

 from 0-0016 to 0*002 inch long, and 0*0008 inch broad 

 (PL VI. figs. 14, 16) : each sheaf appears to represent a cell, and 

 the spicules siliceous rhaphides within it ; the unmetamor- 

 phosed protoplasm of the sheaf is chiefly accumulated in a 

 layer at each end ; one of these layers contains a nucleus 

 with a spherical nucleolus. With age the trichites appear to 

 become separate and are freed from their surrounding enve- 

 lope. Their length is the same as that of the bundle which 

 they form. 



Hub. Marine. 



Loc. Kors fiord, Station 23, depth 180 fathoms. 



In transverse section the sponge is seen to consist of an 

 internal ••mark" (body-substance), separated by a layer of 

 crypt-like cavities from an external well-marked cortex 

 (PL VI. fig. 2). The cortex is about -^ inch thick ; its lower 

 half consists of a layer of bluish-white translucent tissue of 

 great toughness and elasticity, and bearing a superficial re- 

 semblance to cartilage. 



The " mark " is of a yellowish-grey colour, and traversed 

 by canals which branch and become smaller towards the sub- 



Ann. & Mag. Nat. Hist. Ser. 5. Vol. v. 10 



