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



exclusively Radiolarian tests ; in Cerelasma lamellosa (from Station 216a) partly 

 Globigerina shells and their fragments, partly siliceous spicules of sponges and mineral 

 particles. The majority of the xenophya have a peculiar horny envelope, a thin-walled 

 yellow or brown sacculus of spongin. Some of the xenophya (probably those which 

 were most recently incorporated) lie immediately in the transparent maltha, and possess 

 no spongin-envelope. It seems as though the thickness of the sacculi increased with age. 

 The spongin-sacculi are so connected with the branched lamellae of the skeleton that 

 these latter may be regarded as connecting bands between the former. 



The canal-system of Cerelasma seems to be similar to that of Spongelia, with large 

 flagello-ehanibers ; in the two deep-sea species, however, which I have examined, it was 

 not sufficiently well preserved. In the preliminary examination I was inclined to 

 regard as peculiar canals of the sponge the reticulated canal-system, filled with dark 

 phseodift-like masses, which I afterwards recognised as the hydrorhiza of a symbiotic 

 Hydroid (Stylactis or a similar Spongoxenia). The strong chitinous tubes of this latter 

 in Cerelasma seem to replace the main spongin-fibres of Spongelia. 



Probably to this genus belongs also the Keratose sponge which Polejaeff has described 

 as Psammopemma porosum in his Eeport on the Keratosa (p. 48). He says that the 

 foreign enclosures of this species possess a thick envelope of horny substance, 

 " occasionally with very conspicuous outgrowths " (p. 49). The true Psammopemma 

 forms no spongin at all. 



Cerelasma gyrosphsera, n. sp. (PL VI. figs. 1-5). 



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

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

 well-preserved Radiolarian shells. 



Sponge a globular framework, with maeandric surface, composed of numerous 

 cylindrical, anastomosing, convoluted branches. No distinct dermal membrane. Pseudo- 

 skeleton composed almost exclusively of Radiolarian tests. 



Exterior. — The body of the single well-preserved specimen is nearly spherical, 

 slightly flattened on the basal side, where it has been attached. The diameter of the 

 globe is between 60 and 70 mm., 66 on an average. The whole surface is similar to 

 that of a gyrencephalon mammalian cerebrum, numerous curved gyri, and between them 

 deep sulci, being turned in all directions. Closer examination shows that this aspect is 

 produced by numerous cylindrical branches, which form a reticular framework by 

 frequent anastomoses. The length of most of the branches is between 6 and 9 mm., the 

 thickness 3 to 4 mm. The sponge, as preserved in spirit, is rather soft and fragile ; when 

 dry it is rather hard. The colour is dark brown. The surface of the sponge is rough 



