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



Xenophya. — The foreign bodies which compose the pseudo-skeleton of this, the largest, 

 species seem to offer a new argument in favour of my opinion, that such a pseudo- 

 skeleton is constructed, in the Psammospongise as well as in other animals (for instance, 

 in the Physemaria, &c), with a certain amount of selection of materials, for the skeleton 

 of the thick ribs approaches that of Stannophyllum globigerinum, whilst that of the 

 thin membrane between them is more like that of Stannophyllum radiolarium. 



Stannophyllum globigerinum, n. sp. (PI. I. figs. 5A-5C). 



Habitat. — Station 271 ; depth, 2425 fathoms; bottom, Globigerina ooze. 



Sponge with a flabby, white, arenaceous leaf of subovate or triangular outline, the 

 tapering base of which is supported by a conical pedicle. Surface coarsely granular, 

 friable, without radial ribs, but often with more or less distinct concentric zones. 

 Skeleton composed mainly of calcareous Globigerina ooze, the shells and fragments of 

 which are larger in the two cortical faces, smaller in the medullar mass between them. 

 Spongin-fibrilla3 very unequal in size, many coarser and branched between the interwoven 

 finer ones. 



Stannophyllum globigerinum is the opposite end in the series of continuous links 

 which are presented by the five species of this genus, beginning with the coriaceous 

 Stannophyllum zonarium. In contrast to this latter the true fibrillar skeleton is here 

 very weak, especially in the dermal plates, and the main mass of the arenaceous leaf is a 

 pseudo-skeleton, composed almost entirely of Globigerina ooze. Intermingled between 

 the shells and fragments of Globigerina and Pulvinulina there occur many small 

 siliceous shells of Eadiolaria, in far smaller quantity, however, than in the other four 

 species. The spongin-fibrillse which support the cementing maltha are of very unequal 

 and irregular shape, and are most irregularly interwoven in all directions. There are 

 many very thick fibres, 0"006 to O'Ol mm. in diameter and more, and in these the 

 medullar or axial thread is twice as broad as the surrounding cortical wall. The thickest 

 fibrillar are often richly branched, and sometimes begin to anastomose (transition to 

 Psammop>hyllum). 



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

 are in the majority of the numerous preserved specimens almost wholly calcareous shells 

 of Globigerina ooze, and their fragments ; usually the two parallel dermal plates of the 

 foliaceous body are composed of larger shells, the softer medullar mass between them of 

 smaller shells and fragments ; within this latter is expanded the rich brown network of 

 the symbiotic Hydroid. The scanty maltha between the fibrillse includes often rather 

 numerous Eadiolarian shells, and, in the basal pedicle, sponge spicules. 



External Form. — The flabelliform body of Stannophyllum globigerinum is easily 



