422 COLLECTIONS FROM MELANESIA. 



rather brittle, white, marked (at any rate on the stem) on its inner 

 surface by closely-set elongate or reticulate ridges ; covered by a 

 thin, wrinkled, paper-like, pale yellow-brown membrane. Branches 

 given off towards end of stem, in succession, in one plane ; 7-8 

 millim. in diameter at bases, slightly less towards apices. 2") to 60 

 millini. ( 1 to 2] inches) long; cylindrical at base, becoming compressed 

 at apex into flattened subcircular or knife-like expansions, about 

 10 to 12 millim. in width and 1*5 millim. in thickness ; the free ends 

 often (if not always) imperforate. Skeleton of cortex a rather close 

 Halichondrioid network, with meshes - 07-"14 millim. wide, fibre 

 3 to 6 or 7 spicules broad. Main skeleton below cortex coarsely 

 reticulate with immense aggregations of spicules into coarse spiculo- 

 ribre. Sarcode in axial tissues brown, transparent, in cortex 

 almost colourless. Spicules smooth acerate, tapering gradually to 

 sharp points from about seven diameters from ends ; size *22 by *0098 

 millim. 



Hab. Thursday Island, Torres Straits, 4-5 fms. ; bottom mud. 



A single specimen, 175 millim. (7 inches) long, composed of two 

 laterally fused specimens. One end is broken across, and shows the 

 interior to be filled with flocculent spiculo-tissue ; it is thus doubtful 

 whether this end bore any tubes. This species differs, in its very 

 drawn-out form, from all the described species except, perhaps, 

 Phloeodictyon hondurasense, which is known only from a tubular 

 fragment ; but the spicules of that species are considerably smaller 

 than those of this form, viz. only '16 by *008 millim. 



No Chalinoid or even Esperia-\ike fibre appears to occur in any 

 part of the sponge. 



57. Rhizochalina canalis. 

 (Plate XXXIX. fig. F ; Plate XLI. fig. r.) 



Simple, unbranched, cylindrical tubes, straight or slightly bent near 

 middle. Diameter at middle about 10 millim. (in large specimens), 

 gradually (sometimes very slightly) decreasing towards ends ; ends 

 finger-like, closed, 3 to 4 millim. broad. Surface somewhat uneven. 

 Vents apparently represented by circular perforations of cortex, 

 '5 to -8 millim. wide,- few, scattered. Cortex in dry state hard, rather 

 brittle, slightly compressible towards ends, dense ; colour greyish ; 

 thickness about *7 millim. ; outer layer hard, about '2 millim. thick ; 

 inner layer bast-like, closely reticulate, about "3 millim. thick. Axial 

 substance ? Skeleton of cortex composed of very strong vertical 

 spiculo-fibres 5-12 spicules broad, interlacing closely at the surface 

 to form the hard outer layer ; they are about *14 to *18 millim. apart 

 and about - 7 millim. long at the thickest part of the cortex, being 

 met at their inner extremities by a strong secondary fibre (parallel 

 to the surface) about 10 spicules broad. Sarcode pale brown, trans- 

 parent. Spicules smooth acerate, becoming rounded off (rather than 

 tapering) to sharp points from about four diameters from ends; sue 

 •27 by 014 millim. 



