34 4 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The choanosomal skeleton is a feltwork of megascleres aggre- 

 gated, in part, into dense but vaguely denned spiculo-fibers, between 

 which are abundant spicules; the fibers, or tracts, cross and fuse 

 in irregular fashion; the skeleton as a whole is close (dense); 

 a little spongin here and there cements the spicules together. The 

 megascleres are styles, the head sometimes slightly tylote, G00-700 

 by 16-20 \i. 



The ectosome is occupied by a conspicuous and compact layer, 

 varying in thickness from 0.7 to 3 mm., of megascleres crossing in 

 all directions. The megascleres are like those of the choanosome. 

 This dense "cortex" is traversed by narrow tubular canals, more 

 or less radial to the surface; those in the piece examined were a 

 fraction of a millimeter wide and 2-4 mm. apart. 



At the surface are small, radially placed st}des (sometimes sub- 

 tylote), imperfectly arranged bouquet-fashion, the points project- 

 ing; these spicules, in places at any rate, are abundant enough to 

 form a continuous stratum; they measure 250-450 by 6-10 [x. 



There is the usual dermal crust of spirasters. These are 10-12 y. 

 long ; axis long and curved, probably always spirally, the microscopic 

 image showing two or sometimes only one curve; rays numerous, 

 short, stout, blunt, distributed as usual along the length of the 

 axis. 



Under S. vagabunda Ridley, 1884 (p. 468), described sponges 

 from Torres Straits, Trincomalee, and Ceylon, which were massive, 

 "tending to grow up into large nodular elevations, which may 

 bear one or more vents." The interior is made cavernous by wide 

 canals. There is a strong "cortex," about 0.8 mm. thick, formed 

 by intercrossing megascleres. The megascleres are tylostyles 600 by 

 20 [x, or (in var. trincomaliensis) scarcely tylote at all and about 13 

 [ji thick ; spirasters delicate and long, 32 n long, with fairly numerous 

 short and rather blunt spines. The largest specimen measured 225 

 nun. by 130 mm., with a thickness of 60 mm. Ridley calls atten- 

 tion to the characteristic and relatively constant external appearance 

 of the species. 



Dendy, 1905 (p. 122), extends the idea of the species by describ- 

 ing several varieties from Ceylon. In one variety (trincomaliensis) , 

 the surface elevations are digitate processes about 23 mm. long, 

 excavated by the exhalent canals, which are "extremely narrow" 

 (sponge was perhaps greatly contracted). The megascleres form 

 some, at an} r rate, surface brushes. Megascleres are tylostyles and 

 styles about 620 b}' 9 n; spirasters 12 \x. long, with blunt rays (blunt 

 in all spicules?). In another variety (p. 124) the spirasters may 

 reach a length of 48 \l. Dendy merges several species. 



Topsent, 1893, describes a variety from the Gulf of Tadjoura, 

 and (1918) suggests some fusion of species. 



