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



and the origin of the numerous holes which pierce its leaf. But this as well as the 

 characteristic lobulation of the distal margin may be due also partly to the mode of 

 growth, which follows that of the symbiotic Hydroid, partly to the different development 

 of the spongin-fibrillae (compare p. 64). 



The Spongoxenise, or the different forms of symbiotic Hydropolyps, which are always 

 present in Stannophyllum, expand in the soft medullar mass between the two parallel 

 dermal plates, which may be separated more or less easily from the former. The 

 hydranths seem to proceed usually from the distal margin of the flabelliform leaf, but 

 sometimes also from its two faces and also from the base of the pedicle. Usually the 

 imperfect state of preservation prevents the accurate examination of the disposition and 

 structure of these symbiontes, but in a few specimens (principally of Stannophyllum 

 globigerinum) they were well preserved and could be recognised as two species of 

 Stylactella (spongicola and abyssicola, PI. II. figs. 6, 7), compare below p. 78. The canal- 

 system of Stannophyllum, unfortunately, is in most of the specimens badly preserved. 

 I was able, however, to recognise in all the species of Stannophyllum the small dermal 

 pores of the surface, but not with satisfaction the larger openings, which may be regarded 

 as oscula. In Stannophyllum zonarium there are series of larger openings (twice as 

 broad as the usual pores) in the thickened proximal margin of each zone ; in Stanno- 

 phyllum globigerinum sometimes apparent oscula are scattered on the two faces of the leaf, 

 but in the other species they were not distinctly recognisable. It may be that the water 

 entering by the pores of the two parallel faces issues by the oscula of the distal margin 

 (compare PL IV. figs. 7, 8). The internal canal-S3'stem is of variable shape. Larger or 

 smaller subdermal cavities seem to lie immediately below the dermal plates, and to be 

 connected with groups of flagello-chambers, which are disposed in the spongy medullar 

 substance ; these, however, were not distinctly recognisable (compare PL II. figs. 3, 4). 



Stannophyllum zonarium, n. sp. (PL I. figs. 1A-1C ; PL II. figs. 1-4). 



Habitat. — Tropical Pacific, Station 271; September 6, 1875; lat. 0° 33' S., long. 

 151° 34' W.; depth, 2425 fathoms; bottom, Globigerina ooze, containing many 

 Radiolaria. 



Sponge with an elastic brown coriaceous leaf of subcircular or kidney-shaped outline, 

 with a thin and flat pedicle. Distal margin semicircular, integral. Surface soft, 

 velvet-like, without branched ribs, but with distinct concentric zones of subequal breadth 

 parallel to the distal margin. Skeleton composed mainly of interwoven bundles of 

 spongin-fibrillse, and forming a dense felty network, in the meshes of which many shells 

 of Radiolaria and a few fragments of Globigerina are imbedded. 



Stannophyllum zonarium is the most elastic and flexible among the species here 



