SPONGES 167 



a branch. The slender cylindrical portions, and the vesicles too. are now more or less 

 hollow, but they contain the remains of the coarse skeleton network and a certain 

 amount of decomposed soft tissue. Thus, in the present condition of the specimens, 

 the outer wall of the sponge forms a thin but firm shell enclosing a wide cavity in 

 which lie the remains of the choanosome. How far the sponge was hollow in life 

 cannot now he ascertained. The colour (in spirit) is dark brown throughout, with 

 a slight purplish tinge on the surface. The surface is smooth, but has a very 

 characteristic tessellated appearance, caused by the very stout sub-dermal reticulation 

 of spicular fibre showing through the thin dermal layer. Each specimen has a total 

 length of about 27 millims. The largest vesicle measures about 11 millims. by 

 !> millims., and the slender cylindrical portions are about 4 millims. in diameter 

 (sometimes rather less). 



The main skeleton forms a very wide-meshed reticulation of very stout spicular 

 fibre, occupying the interior of the sponge ; the meshes being very irregular in shape 

 and size. The diameter of the fibre, which appears to be composed entirely of very 

 closely packed megascleres, is about 0'165 millim. There is a sub-dermal reticulation 

 of similar fibre with roundedly polygonal meshes, the meshes being about 1 millim. in 

 diameter. This supports the dermal skeleton (Plate XL, fig. 8), which is very well 

 developed and extremely beautiful, consisting of a single layer of strongyla of various 

 lengths lying tangentially side by side as closely packed together as possible, with a 

 few much larger oxea, or sometimes styli, intermingled with them. 



Spicules. (1.) Oxea (Plate XL, fig. 8, o, o, u) ; rather long and only moderately 

 stout ; slightly curved, usually sharply but sometimes rather abruptly pointed at each 

 end; size about 0*3 millim. by - 009 millim., but -variable. Abundant in the fibres of 

 the skeleton and scattered in the soft tissues between, where numerous very slender, 

 hair-like forms, possibly young, also occur. 



(2.) Strongyla (Plate XL, fig. 8, s, s) ; cylindrical, more or less curved, and evenly 

 rounded off at each end; size extremely variable, from 0'04 millim. by (V005 millim. 

 to 0"1 millim. by 0'007 millim., or perhaps more. Characteristic of the dermal skeleton, 

 but also found in the spicular fibres and soft tissues of the choanosome. 



(3.) Palmate isochelre (Plate XL, fig. 9), about - 016 millim. long ; very similar to 

 those of Desmacidon conulosa, as figured in the Report on the "Challenger" 

 Monaxonida ; numerous. 



(4.) I have also seen one "birotulate" of about the same length as the ordinary 

 isochelaB ; with very slender and apparently straight shaft and short umbrella-like 

 ends with minutely dentate margins. Whether or not this forms a constant element 

 in the spiculation I am not prepared to say, but its presence is very interesting in 

 view of the normal occurrence of such spicules in the genus Amphiastrella. 



This species differs from Histoderma singaporense (Carter) chiefly in external 

 form, but also in the more slender character of the oxea. 



Lixix;i?ex, however, has described (86), under the name Rhizochalina singaporensis 



