new Recent Pharetronid Sponges. 511 



formly granular appearance. An oscule, just visible to the 

 naked eye, is seen as a dark point near one end ; two smaller 

 oscules occur, but are not discernible without a lens. 



Under a lens, the surface shows small polygonal areas, 

 each bounded by 5-7 small tubercles ; the latter push up the 

 dermal membrane, which is sunk a little in the areas them- 

 selves. The largest oscule is oval, slightly raised, "28 x 

 •15 mm. in its long and short diameters, and surrounded by 

 nine tubercles ; in 1'act, it resembles two smaller pore-areas 

 run together. The pore-areas are about }■ of a millimetre in 

 diameter, and in several a single large pore was visible in the 

 centre of the covering dermal membrane. 



A vertical section shows a vertical series of honeycomb- 

 like cells separated from each other by horizontal perforate 

 floors (and ceilings) and by vertical imperforate walls. A 

 vertical section, complete from base to surface, with four 

 superposed " cells " was *665 mm. thick. 



The honeycomb cells are cylindrical, and the vertical 

 section shows rectangular areas (150 //, longx 120 /j, broad), 

 just as the same section of a solid cylinder would; similarly 

 the horizontal section shows circular areas. 



The sponge is attached to the substratum on which it is 

 growing by a thin floor of fibrillar cement. The vertical 

 pillars, which are the main scaffolding, arise from this floor 

 and pass up to the surface, where they end in the tuberculated 

 knobs. 



From each pillar there radiate out three wings, which meet 

 similar wings from other pillars, a median raphe showing 

 the line of junction. Accordingly each pillar has six sides, 

 three concave ones forming segments of the cylinders they 

 help to form, and three straight band-like edges forming the 

 vertical edges of the wings. The direction of the tibrillae 

 marks off wings from opposing pillars, the fibrillse radiating 

 out more or less obliquely outwards and upwards from the 

 central axis of a pillar to the raphe. 



The floors (and ceilings) which exhibit fibrillar structure, 

 show also five or more radial raphe lines where sections of 

 flooring from each pillar are joined ; in the centre of the 

 floor is a circular hole, which may be reduced to a fine slit. 

 Very fine concentric lines are seen on the floors. 



A surface view (PI. XV. fig. 13) shows well the tubercles 

 each with three thick wings or bars radiating out below them, 

 to meet similar bars. 



The fused bar shows the median raphe and the opposing' 

 fibrill*. P P \ ° 



A very careful examination under all powers and lights 



