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



fibres, which partly connect, partly include, the xenophya. These foreign bodies are in 

 the latter species principally siliceous spicules of different sponges; in the first species 

 principally Radiolarian tests, and in the second species both these forms of xenophya are 

 found. The chitinous tubes of the hydrorhiza of the symbiotic Hydroids replace in all 

 • the three species the stout main fibres which are characteristic of Spongelia. 



Psammophyllum reticulatum, n. sp. (PI. V. figs. 1-4). 



Habitat.— Tropical Pacific, Station 198; October 20, 1874; lat, 2° 55' N., long. 

 124° 53' E. ; depth, 2150 fathoms ; bottom, blue mud. 



Sponge foliaceous, reniform, pedunculate, very thin, felty, with undulate distal 

 margin. Surface reticulate, without concentric zones. Framework of the spongin-fibres 

 very scanty and loose, mainly composed of very thin and solid anastomosing fibres, which 

 connect siliceous spicules of different sponges and other xenophya. The same foreign 

 spicules also fill up the maltha. 



Psammophyllum reticulatum has the shape of a broad reniform leaf, which attains, in 

 the largest specimen preserved, a height of 50 to 60 mm. and a breadth of 80 to 90 

 mm. or more. The majority of the specimens preserved are about half that size or less ; 

 there are a few small leaves in the collection, which are only 3 to 4 mm. in height and 5 

 to 6 mm. in breadth, but the form and structure is the same as in the largest leaves. 

 The thickness of the leaf is between 1 and 5 mm., usually 2 or 3 mm., and nearly equal 

 throughout the whole extent, but several leaves are thinner in the middle part (only 

 0"4 to 0*5 mm.) and thicker on the club-shaped base of the pedicle (7 or 8 mm.). The 

 pedicle is cylindrical, usually about half as long as the leaf itself, gradually broadening 

 toward both ends ; the basal end is thickened and expanded into an irregular foot-plate 

 for attachment. 



The colour of the leaves is brown, the consistence very soft and fragile, little elastic. 

 The entire surface is felty or woolly, and the aspect of the body at first sight is that of a 

 thin felt-sole or hair-sole. It is very loose in texture and easily torn to pieces. The 

 woolly aspect and the felty consistence of the surface is produced by the numerous large 

 spicules of siliceous sponges everywhere prominent and matted together. 



Symbiontes. — The characteristic reniform leaf-shape of the sponge is evidently 

 produced by the dense network of the symbiotic Hydropolyp (Spongoxenia), which is 

 growing in a vertical plane, like a Rhipidogorgia. The sponge itself is only a thin 

 woolly mantle, which covers both sides of the foliaceous polyp-corm and fills up the 

 meshes of its loose network. The chitinous tubes of this latter are cylindrical, often 

 varicose, 0"1 to 0'2 mm. broad; the meshes between them are 1 to 3 mm. in diameter. 

 The tubes are irregularly curved, broadened on the nodal points of the network, and 



