110 CHALINOPSILLA. 



The sponge is pretty hard, fairly compressible, and very inelastic. The colour 

 is lighter or darker brown in the living state ; dry skeletons of C. a. micro- 

 j)ora are yellowish, of other varieties dirty brown. 



The surface-skeleton consists of a network of threads composed of foreign 

 bodies (sand-grains), which are held together by a very small and hardly per- 

 ceptible quantity of spongin. The fibres are 0*1 millim. thick and the meshes 

 0*5 millim. wide. 



The snpporting-slceleton consists of stout and knotty main fibres, which are, 

 on an average, 0"2-l*6 millim. thick and 0"9-l*4 millim. apart; they are 

 parallel, and extend longitudinally in the axis and central portion of the sponge, 

 curving gracefully in a plumose fashion towards the surface. The connecting- 

 fibres are 0*08 millim. thick, and on an average 1 millim. apart ; they are 

 perpendicular to the main fibres and scarcely at all branched ; generally, 

 however, divided at their bases of attachment into two or three roots. The 

 foreign bodies forming the surface-skeleton are small sand-grains, about 

 0*05 millim. in diameter ; they are packed very closely. In the main fibres 

 of the supporting-skeleton scattered aiid large sand-grains are met with, on 

 an average 0*25 millim. thick and 0*3 millim. apart, always situated axially. 

 In the connecting-fibres very small monaxonid siliceous spicules are some- 

 times observed ; these form a single axial row. They are often fragmentary, 

 but sometimes also intact. Often they make the impression of proper spicules : 

 oxea, 0-07 millim. long and 0*006 millim. thick, rather abruptly and sharp 

 pointed. As, however, these entire spicules always occur together with broken 

 fragments, I am inclined to consider them as foreign. 



Chalinopsilla arhorea imitates various species of Chalininse, and the specimens 

 always grow in close proximity to the sponges imitated. The spicules found 

 in the connecting-fibres of the CTiaUnopsilla arhorea varieties are very similar 

 to those of the imitated Chalininse, and I believe they derive their spicules 

 from decayed specimens of the species they imitate. 



Chalinopsilla arborea, var. macropora, Duchassaing & Michelotti. 



Callyspongia tenerrima, Duchassaing et Michelotti, " Les eponges de la mer 

 Caraibe," p. 57 (1864). 



Dactylia chaliniformis, H. J. Carter, " Descriptions of Sponges from the 

 Neighbourhood of Port Phillip Heads, South Australia," Annals and 

 Magazine of Natural History, ser. 5, vol. xv. p. 309 (1885). 



Dactylia palmata, H. J. Carter, I. c. p. 310. 



Dendritic sponges attached by a stout stem, which attains a length of 50 

 millim. in some specimens, but appears quite short and rudimentary in 

 others. The stem is generally about 15 millim. thick. From its upper end 



