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



similarly as in Stannophyllum venosum (PI. I. fig. 4). The ribs are lighter in colour, 

 grey or whitish ; they disappear in the distal part of the leaf, which exhibits distinct concen- 

 tric zones of nearly equal breadth (3 to 4 mm.). The zones are more prominent than in the 

 following species, and more thickened in the proximal part, so that the vertical section 

 is cuneiform (PI. IV. figs. 7, 8). Each zone therefore covers with its thickened 

 proximal edge the thinner distal part of the neighbouring proximal zone; the thickened 

 edge exhibits an irregular row of large openings, probably the oscula (fig. 7, o), whilst 

 the felty dermal membrane of the surface is pierced by the smaller dermal pores (fig. 7, p). 

 The outermost distal zones exhibit oscula also on the two faces (fig. 8, o). Scattered in 

 some parts of the mesoderm were found amoeboid egg-cells, similar to those of other 

 Keratosa (PI. V. fig. 5, e). 



Symbiontes. — The spongy parenchyma between the two parallel dermal plates is 

 traversed by numerous anastomosing cylindrical tubes, which form a rather dense net- 

 work. These chitinous tubes belong to the hydrorhiza of a symbiotic Hydroid, 

 Halisiphonia spongicola (PI. IV. fig. 9). After long continued researches, I was suc- 

 cessful in finding in some portions of the sponge the club-shaped gonangia (fig. 9, g) as 

 well as the urn -shaped hydro thecse (fig. 9,p) of the symbiotic Spongoxenia. The cellular 

 contents of the chitinous tubes were rarely distinct (PI. V., fig. 5, h) ; usually they were 

 destroyed, their remains forming a dark granular mass of an olive or brown colour. 



Xenophya. — The foreign bodies which compose the pseudo-skeleton in this species 

 are more varied than in the preceding and following species. Siliceous spicules of 

 sponges, tests of Radiolaria, and various mineral particles characteristic of the red clay, 

 occur intermingled. They are partly crowded in the clear maltha, partly enclosed by 

 the meshes of the network of the spongin-fibrillse (PI. IV. fig. 6, r), and the smaller 

 xenophya are enclosed in the horny fibres, as in Spongelia. 



Horny Skeleton. — The spongin-fibres in this species are more developed than in any 

 other Deep-sea Keratosa here described. They form a dense irregular network, exhibit 

 numerous ramifications and anastomoses, and are of very unequal thickness (PI. IV. 

 fig. 6,/). The thinner fibrillse (O'OOl to 0"01 mm. in diameter) are equal to those of 

 Stannophyllum, whilst the thickest fibres (0"02 to - 06 mm.) approach those of Spongelia. 

 The axial thread is very distinct. 



Psammophyllum annectens, n. sp. (PI. IV. figs. 1-4). 



Habitat.— North Pacific, Station 244; June 28, 1875; lat. 35° 22' N., long. 169° 

 53' E. ; depth, 2900 fathoms ; bottom, red clay. 



Sponge foliaceous, reniform, pedunculate, rather compact and elastic. Surface with 

 concentric zones of equal breadth. Framework of spongin-fibres very irregular, 



