22 HOLASCUS EDWARDSII. 



The larger of the two separate root-tufts is rectangularly bent near the 

 middle of its length. One limb, which evidently formed the stalk of the sponge, 

 is 60 mm. long, cylindrical, straight, and throughout about 14 mm. thick. The 

 other limb, which formed the root, is 70 mm. long, conic, and attenuated to a 

 fine point. The smaller separate root-tuft is similar but more uniformly curved. 



The colour of the sponge-body proper, that is the tube, is, in spirit, nearly 

 dark brown. The root-tufts are colourless. 



The skeleton. A network with rectangular meshes composed of large, stout- 

 rayed pentactines, held together by slender-rayed comitals, forms the main 

 support of the tubular sponge-body. The large pentactines have a short apical 

 and four long lateral rays; two of the latter, the two opposite ones, are usually 

 markedly longer than the other two. These pentactines lie side by side in a 

 single layer in the choanosome of the tube-wall; their apical rays are directed 

 radially outwards; their lateral rays extend paratangentially, the longer ones 

 longitudinally, the shorter ones transversely. The distances between the centres 

 of these pentactines are much smaller than the length of their lateral rays, 

 which consequently cross each other repeatedly. Slender-rayed diactine to 

 hexactine comitals accompany these pentactines in large numbers. As the 

 rays of these spicules closely adhere to the rays of the pentactines, and as dif- 

 ferent rays of the same comital are often attached to rays of different pen- 

 tactines, the latter are firmly held together and in position by the former. 



Small hexactine megascleres, rhabds, microscleres, and siliceous skeletons 

 of foreign organisms also occur in the choanosome. 



The small choanosomal hexactine megascleres appear to be much more 

 abundant in the lower than in the upper parts of the tube-wall. Quite low down, 

 in the region where the tubular body passes into the root-tuft, they form dense 

 masses. 



Of choanosomal rhabds other than the diactine comitals of the large 

 pentactines I have observed two kinds, centrotyles and exceedingly slender, 

 thread-like rods. The centrotyles are of varying size, and the large ones usually 

 accompanied by smaller ones arranged round them comital-fashion. The 

 slender thread-like rhabds were found only in the choanosome of the small 

 specimen. 



The microscleres are oxyhexasters, hemioxyhexasters, microoxyhexasters, 

 graphiocomes and (?) ring-shaped sigms. Of the three first named, which must 

 be considered as different varieties of the same kind of spicule, the oxyhexasters 

 are by far the most numerous; the hemioxyhexasters are rather, the micro- 



