236 

 Family Placospongidae. 



Genus Placospongia (Gray). 



Placospongia labyrinthica, sp. n. 



Plate v., Fig. i, la, ib. Plate VI., Fig. la-f. 



Sponge massive. The small circular osciiles, .75 mm. in 

 diameter, restricted to circular, oval, or irregular plaques with 

 slightly raised margin and depressed area, the plaques being for 

 the most part aggregated over a certain area. 



Circular pores, .4 mm. in diameter, more or less uniformly 

 distributed over an extensive rough hummocky area. The 

 surface, where it is devoid of pores and oscules, quite smooth. 



Colour of specimens (in spirit), pale yellow, with a faint 

 purplish tinge over the oscular areas. 



Skeleton composed of a dense pseudo-sterrastral cortex, and 

 of labyrinthine walls of the same structure dividing the body 

 mass into numerous cavities, some being small and spherical, 

 others large and elongated. Sterrasters scattered in the soft 

 tissues, also megascleres and microscleres. 



Spicules. Megascleres. — Sub-tylostyle, or style thickened at 

 the base, 2125 x 36 /«, slightly curved, gradually tapering from 

 the base to the usually blunt point. 



Oxea and strongyle, 2425 x 45 /x, curved at the centre. 



Sterrasters varying in size up to 160 x 100 /«, ellipsoidal. 



Microscleres. — Somal chiaster 16 a*, with 9-1 1 actimes and a 

 small centrum. 



Another kind (not figured), 32 m in diameter, with five 

 roughened truncate actines and a small centrum. 



Pycnaster (or small spheraster), mostly ectosomal, 6 to 14 ft 

 in diameter. 



Locality A. — East London coast, 85 fathoms. 



This remarkable species is represented by two large massive 

 specimens. The first is massively flabellate, slightly cleft at 

 the thick rounded margin so as to form three thick lobes ; the 

 height is 10 cm., the width 14 cm., and thickness 8 cm. The 

 oscular areas vary from i to 2.5 cm. in diameter ; a ridge 

 surrounds the extensive poral area. The second specimen, 

 which slightly resembles in shape a kneeling camel, is 11 cm. in 

 thickness ; a sharp " dorsal " ridge runs along the upper edge ; 

 one side (the " near " side) is smooth and imperforate ; the 

 other is provided with oscular plaques over one-half, while 

 the rough poral region occupies the other. 



Both specimens have been torn from their attachment and 

 reveal at their bases the broken labyrinthine cavities. 



I was unable to find a definite sterrastral axis. On making 

 vertical sections, the smaller spherical chambers were in one 



