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



(Stannophyllum), whilst all the others are secondary wings, budding from its two parallel 

 faces (compare PI. I. fig. 5B). The internal structure as well as the external form of 

 these leaves are the same as in the ancestral Stannophyllum, and the material of the 

 pseudo-skeleton is variable in a similar way. 



Two different species of Stannarium were found in the Challenger collection, the 

 first (Stannarium alatum) with free wings, the second {Stannarium concretum) with 

 united wings, so grown together that funnel-shaped cavities remain between them. The 

 pseudo-skeleton of the former is composed mainly of Radiolarian ooze, while in the latter 

 more or less Globigerina ooze is intermingled. The spongin-fibrillae are more regular, 

 equal, and thin in the former, coarser and unequal in the latter, so that the differences 

 between these two species are similar to those between their ancestral forms, Stanno- 

 phyllum radiolarium and Stannophyllum globigerinum. 



Stannarium alatum, n. sp. (PI. III. figs. 6-9). 



Habitat. — Central Pacific, Station 272; September 8, 1875; lat. 3° 48' S., long. 

 152° 56' W.; depth, 2600 fathoms; bottom, Eadiolarian ooze. 



Sponge rather consistent, with several vertical, free, foliaceous wings, which are not 

 grown together, and arise from a primary nabelliform leaf. Skeleton composed mainly 

 of Radiolarian ooze. 



There are several specimens of Stannarium alatum, varying in diameter from 

 30 to 60 mm. From a thick basal pedicle arises vertically a primary flabelhform leaf 

 {Stannophyllum), and this produces by lateral budding several secondary leaves, which 

 also stand nearly vertical. Usually there are two larger secondary leaves arising obliquely 

 from the two sides of the primary leaf, so that the sponge seen from above represents 

 an irregular four-winged cross (fig. 8). Sometimes several smaller lateral wings arise 

 between the larger. The wings are ovate, or semicircular, of the same thickness as the 

 primary leaf, between 1 and 2 mm. The distal margins are integral or slightly lobulate. 



The surface of the leaves is finely arenaceous (from the conglomeration of Radiolarian 

 shells), and at the same time felty (from the irregular web of the fine spongin-fibriUse). 

 Innumerable very small pores pierce the thin dermal membrane, which may be stripped 

 off from the dense,, felty, medullar mass. This is rather compact, traversed by the same 

 canal-system and the same network of the symbiotic Hydroid as in the ancestral Stanno- 

 phyllum radiolarium. 



Skeleton, — Amongst the xenophya or foreign bodies which compose the pseudo- 

 skeleton, siliceous Radiolarian shells are predominant, but sometimes spicules of siliceous 

 sponges and also fragments of calcareous Globigerina shells are intermingled, the latter 

 mainly in the basal pedicle. All the xenophya are surrounded and connected by the 



