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



Genus 11. Stannoma, n. gen. 1 



Definition. — Stannomidse with arborescent body, divided into numerous free or 

 anastomosing cylindrical branches. 



The genus Stannoma differs from the other Stannomidse in the arborescent form of 

 the body, which is like a small tree or coral stock. The ramifications of the corm are 

 sometimes regular and dichotomous, at other times irregular. 



Two species of Stannoma were found in the Challenger collection, both taken at two 

 neighbouring stations in the Central Pacific, viz., Station 271 (2425 fathoms) and 

 Station 272 (2600 fathoms). The Radiolaria in the ooze covering the bottom at these 

 two stations make up the pseudo-skeleton in both species ; the xenophya are imbedded 

 in a scanty clear maltha, which is supported by a dense framework of thin spongin- 

 fibrillee. 



The branches of the arborescent body are cylindrical in both species. They are free 

 in Stannoma dendroides (PI. III. fig. 1), while they anastomose and form a loose network 

 (similar to Clathria) in Stannoma coralloides (PI. III. fig. 5). A transverse section 

 (PI. III. figs. 2, 3) shows numerous brown tubes of the symbiotic Hydroid (h) ; the tubes 

 seem to belong to two different genera (Stylactis, Halisiphoyiia). The branches of the 

 reticular hydrorhiza give a firm support to the arborescent sponge, and between them 

 branch its canals, the course of which could not be made out. The dry Stannoma 

 is very light and friable, the surface loosely woolly and finely sandy ; the dermal 

 membrane which covers the surface of Stannophyllum is absent here. 



Stannoma dendroides, n. sp. (PL III. figs. 1-4). 



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

 ooze. Station 272 ; depth, 2600 fathoms; bottom, Radiolarian ooze. 



Sponge arborescent, irregularly branched (partly dichotomous, partly polychotomous), 

 with slender cylindrical branches tapering towards the conical distal end. Branches 

 free, without anastomoses. 



The body of the tree-like sponge is 30 to 50 mm. high, 20 to 30 mm. broad, very 

 soft and flexible, in the dry state friable. The short stem, 10 to 20 mm. in height, 

 3 to 5 mm. in thickness, is either cylindrical or inversely conical, tapering towards the 

 small base, and divided into three to six stout main branches, 3 to 4 mm. in diameter. 

 These divide again into secondary and tertiary branches of varying lengths, between 



1 Stannoma = Cemented body, tniyva^a.. 



