SPOXGIIDA. 601 



its wall about *05 millim. thick, of a fine transparent purple colour, 

 and is composed of a transparent matrix containing closely packed 

 subglobular transparent cells -008 to -013 millim. in diameter, pro- 

 vided with small opaque refringent nuclei; tho lamina) composing 

 the wall of the fibre are readily separated. The dermal membrane 

 is not, as in A. membranosa, traversed by raised thickenings which 

 radiate from the tips of the conuli, but is externally homogeneous 

 and subtranspareht ; it is pale purple in colour and quite thin ; 

 under the microscope it is subtransparcnt, granular and speckled 

 in parts with the less transparent and darker purple nuclei or con- 

 densed pigment-masses, about -005 millim. in diameter, which occupy 

 the centres of large cells. 



Hab. Marie Louise Island, Amirante group, 16 and 17 fms. ; Provi- 

 dence Island, Mascarene group, 19 fms. 



The species appears to be most nearly related to A. carnosa, 

 Schmidt (Spong. Adr. Meer. p. 26, pi. iii. fig. 3), from the Adriatic, 

 and A. cauliformis, Carter (Ann. & Mag. N. H. 1882, ix. p. 270), from 

 the West Indies ; but differs from the former in its far more loosely 

 reticulate skeleton, and from the latter in not having the surface 

 nearly even. It is perhaps identical with the elongated specimens 

 described by Pallas (I. c.) under Spongia membranosa. It differs 

 superficially from the typical form of that species in the closer 

 approximation of the conuli, the more slender habit of the sponge, 

 the smoothness of the dermal membrane, in its minute structure, 

 and in the simple, not compound, character of the skeleton-fibre. 



The larger specimens are slightly compressed laterally, and both 

 measure about 60 millim. (2* inches) in height ; four spirit-speci- 

 mens form the series. 



17. Ianthella flabelliformis. 



Spongia flabelliformis, Pallas, Elench. Zooph. p. 380. 



A macerated fragment agreeing in outward form, so far as it goes, 

 and in the proportions and character of its fibre with the above 

 species. The places in the fibres originally occupied by the purple 

 cells are chiefly represented by vacant spaces, giving a honeycombed 

 appearance to the skeleton-fibre in some parts. 



Hah. Providence Eeef, Mascarene Islands, 24 fms. 



Distribution. See Part I., p. 392, of this Report. 



SILICEA. 



M ON A CTINELLIDA . 



The great abundance of Ceratosa has for its complement a corre- 

 sponding comparative scarcity of Monactinellid Silicea ; this defi- 

 ciency is largely accounted for by the few Ectyonidte collected here 

 as compared with the Northern Australian waters. 



