BPONSIIDA. 389' 



rounding tissues. The paler colour, to the natural eye, of the latter 

 sponge appears to be due to the greater concentration of the pigment 

 within the cells : a similar effect is produced by a similar cause in 

 some Cephalopoda (LoUgo). 



16. Dysidea digitifera. (Plate XLI. flg. C.) 



Curved and anastomosing cylindrical digitations, about 3 millim. 

 in diameter, arising from the upper aspect of an erect, compressed, 

 irregular basal mass, and tapering gradually to pointed ends. Sur- 

 face even, minutely roughened by the presence in the dermis of a 

 coarse, reticulate, horizontal skeleton. Vents few, scattered on main 

 mass of sponge, subciroular, leading deeply into sponge. Texture 

 (in spirit) very friable ; colour pale greyish brown. Main skeleton, 

 composed of large foreign bodies, united by a thin, almost colourless 

 membrane (not visible unless the fibre is broken) ; primary * fibres 

 running approximately at right angles to surface ; secondaries 

 {tertiary of Marshall) approximately parallel to surface, very short ; 

 meshes narrow, about -07 to -09 millim. broad, rounded ; fibres -019 

 to -05 millim. thick. Dermal skeleton formed of fibre similar to 

 that of the main skeleton, about -025 to -055 millim. thick, forming 

 circular or oval meshes, "032 to -09 millim. broad. Sarcode pale 

 greyish brown, rather granular. 



Bah. Albany Island, Torres Straits, 8 fms. 



This is a delicate species, distinguished from aU other described 

 species by its closed digitate processes (those of D. callosa, Marshall, 

 bear vents) ; in being devoid of conuli it differs from most species, 

 but seems to agree with Dysidea kirJcii, Carter (Ann. & Mag. N. H. 

 (5) vii. p. 374), ?Bowerbank. 



Height of sponge 40 millim. (1| inch) ; greatest lateral extension 

 25 millim. (1 inch) ; longest individual digitation, 20 millim. 

 (^ inch). The sponge has grown up amongst and over some speci- 

 mens of Eudendrium. 



17. Dysidea semicanalis. (Plate XLI. fig. B.) 

 A hoUow flattened vertical common stem, giving rise to several 

 vertical cloaoal tubes, some of which are open .on one side (evi- 

 dently formed in some cases by the folding over of surface-ridges), 

 united more or less by their projecting knife-like adjacent edges. Tubes 

 about 60 millim. (2g inches) in greatest length ; mean internal dia- 

 meter about 6 millim. ; contracted at mouth, their walls 3 to 4 millim. 

 in greatest thickness ; inner surface provided with a few shallow 

 pits. Outer surface bearing a few long, but not prominent, ridges 

 running from near base to near the upper end ; surface between ridges 

 even, minutely honeycombed in dry state by small, longitudinally 

 elongated spaces, separated by fibres of dermal skeleton, and about '5 

 millim. in their smaller diameter. Texture, in dry state, rather harsh 

 to the touch, firm but elastic, compressible and somewhat tough. 

 Colour pale yellowish brown. 



* Secondary of Marshall, primary of Hyatt, vertical of Carter. 



