SILICIOUS AND HORNY SPONGES WILSON. 491 



chides, stages in the development of the fibers. Their irregular shape 

 in transverse section constitutes a point of resemblance to P. arabica 

 and Pi keUerl. Altogether it would seem that Aplysina purpurea 

 must be regarded as the type of the genus to which I would in any 

 case refer the Albatross sponge. 



Row (1911, p. 377) refers a Red Sea sponge to A. purpurea. Hent- 

 schel (1912, p. 437) has studied a specimen from the Aru Islands. 

 The individual fibers give very irregular cross sections and are va- 

 riable (same fiber) in thickness, although often 200-300 y. thick, pith 

 occupying nine-tenths or more of total thickness; the compound 

 tibers measuring up to 2 mm. thick. 



The resemblance between the fibers of PsammdplysiUa and Drui- 

 netta Lendenfeld deserves noting. In D. rotunda Lendenfeld, from 

 Australian waters, the fibers show in cross section the same irregu- 

 lar lobose shape and coarse stratification (Lendenfeld 1889, p. 425, 

 pi. 34). In Thiele's D. ramosa, from Celebes, the fibers show the 

 same shape (Thiele, 1899, p. 24, pi. 4). Finally, the resemblance may 

 be noted that is offered by the fibers of Thymosia Topsent {T. guernei 

 Topsent, coast of France, Topsent, 1895, p. 574. pi. 22, fig. 7). 

 This sponge, originally referred by Topsent to the Chondrosidae, is 

 surely a horny sponge, as Lendenfeld (Zoologisches Centralblatt, vol. 

 3, p. 393) has suggested. Lendenfeld refers it to Drulnella. 



Subfamily Stelosponginae 



Stclosiwnginne Lendenfeld, 1889, p. 468. 



Spongidae in which main fibers and connectives are generally 

 distinguishable in the skeletal reticulum. The main fibers may be 

 simple, but are generally more or less fascicular. Between the 

 fascicular fibers, or between the simple main fibers in species with- 

 out fascicles, the skeletal meshes are much larger than in the 

 Eusponginae. 



Genus HIRCINIA Nardo (1834). 



Hircinia Nardo, 1834, p. 714. — Lendenfeld, 1889, p. 526. — George and Wil- 

 son, 1919, p. 166. 



Stelosponginae with filaments in the ground substance and in 

 which the connectives are characteristically attached to the main 

 fibers by diverging roots which extend along the main fiber in one 

 plane. 



HIRCINIA MUTANS. new species. 



Tlate 44, fig. 2 ; plate 52. figs. 2, 4, 6, 7. 



One dried specimen. Locality uncertain; no label. Sponge a 

 cavernous mass, 280 mm. long, 150 mm. wide, and 40-100 mm. thick, 

 which evidently had been attached and in part incrusting over one 



