B90 COLLECIIONS FKOM MELASBSIA. 



Main skeleton forniing rectangular meshes ; primary fibres strong, 

 running at rigtt angles to surface, exhibiting horny margins (which 

 may form as much as one third of total thickness of fibre), about 

 •28 to -35 millim. apart, -1 to -18 millim. thick. Secondary fibres 

 vertical to primaries, at about the same intervals, either without 

 foreign bodies or with only about half to two thirds of the thickness 

 occupied by them ; in the former case -035 to -043 millim. thick, in 

 the latter -053 to -1 millim. thick. Longitudinal fibres {"primary of 

 Marshall) of same structure as primaries, but less homy, -IS to '28 

 millim. apart, -14 to -21 millim. thick, running upwards and spread- 

 ing out somewhat from each other. Dermal skeleton composed of 

 long compound fibres, the primaries running parallel to each other 

 and to the long axis of the sponge, "35 to -43 millim. apart ; the 

 secondaries extended between them at considerable intervals ; pri- 

 maries -14 to "28 millim. broad, secondaries •! to "14 millim., the 

 horny matter of the former usually, of the latter often, obscured by 

 the foreign bodies, which often project much from the fibre. Horny 

 substance amber -yellow. Sarcode amber-yellow, transparent. 

 Foreign bodies of fibres small, chiefly sand. 



Hah. North-east coast of Australia. 



The single specimen is 105 millim. (4i inches) high by 65 miUiiii. 

 greatest width. In its even compact surface it differs from all other 

 Dysidece except B. favosa, Marshal], with which it also agrees in 

 the large development of the tubular form which it exhibits. The 

 strongly horny character of the secondary fibre, however, distin- 

 guishes it from this (as from most, if not all other) species, and 

 allies it to Hircinia. These striking characters, and the good pre- 

 servation of the specimen, seem to warrant its description. 



18. Psammopemma densum, Marshall, var. subfibrosa. 

 (Plate XLI. fig. h.) 



Psammopemma densum, Marshall, Zeitsch. wiss. Zool. xxxv. p. 113. 



Agreeing closely in size and external characters with Marshall's 

 account of this strange form is a specimen in spirit in the present 

 collection. It has the size and almost the shape of a horse-bean, 

 and is of a grey colour. The dermal membrane contains numerous 

 foreign bodies, but is in parts transparent, though fibrillated. Owing 

 to an inferior amount of contained sand, a distinct network of wholly 

 sandy fibres is to bemade out, which Marshall did not find in his speci- 

 mens ; the meshes are round, about -3 millim. in diameter, in the 

 natural state almost fiUed up with sarcode containing foreign bodies. 

 Sarcode very pale brown, subtransparent. The radiating tubes indi- 

 cated iu Marshall's figure (6) appear to me possibly to represent 

 spaces between primaryfibres; butthosefibresinthe present specimen 

 are not straight, but bend right and left to meet the short secondary 

 lines ; thus a vertical section of the sponge exhibits a somewhat 

 honeycomb-like appearance. No trace of horny matter was observed. 



Hab. Thursday Island, Torres Straits, 3-4 fms. 



Distrihution. Tasmania (Marshall). 



