8P0NGIIDA. 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 (Loligo). 



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



Curved and anastomosing cylindrical digitations, about 3 millim. 

 in diameter, arising from the upper asped 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, subcircular, 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 tho 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. 



Hab. Albany Island, Torres Straits, 8 fms. 



This is a delicate species, distinguished from all 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 LirJdi, Carter (Ann. & Mag. N. H. 

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



Height of sponge 40 millim. (14 inch) ; greatest lateral extension 

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

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

 mens of Eudendrium. 



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

 A hollow flattened vertical common stem, giving rise to several 

 vertical cloacal 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. (2^ 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. 



