SILICIOUS AND HORNY SPONGES WILSON. 343 



Hymedesmia Bowerbank in Topsent's sense (1898, 1900) should be 

 designated Timea Gray; also that the designation Hymedesmia 

 Bowerbank should be used for the ectyonine group of species for 

 which Topsent (1892) proposed the name Leptosia, since this group 

 included Hymedesmia zetlandica Bowerbank, the type of Hymedes- 

 mia. Lundbeck (1910, p. 41), Stephens (1912, p. 58; 19156, p. 22) 

 and Hentschel (1912, p. 322) accept Thiele's changes, as do I. 

 Hymedesmia in Topsent's sense of 1898 has, however, the sanction of 

 Topsent's later papers and of Dendy, 1905. Dendy 19216 (p. 142) 

 now accepts Thiele's changes. 



The systematic position of Placospongia is discussed by Vosmaer 

 and Vernhout (1902, p. 16). These authors call to mind that 

 Keller (1891) demonstrated that the so-called sterrasters of this 

 genus develop from spirasters, and that he therefor transferred the 

 genus from the neighborhood of the Geodiidae in the Astrophora 

 to the Spirastrellidae. Keller's move has been generally followed 

 (Vosmaer, Lendenfeld, Thiele, Dendy). 



Genus SPIRASTRELLA O. Schmidt (1868). 



Spirastrella Schmidt, 1868, p. 17. 

 Sponge incrusting, cushion-shaped, massive, or vasiform; in the 

 latter case the two surfaces may be structurally different, the outer 

 incurrent, the cloacal excurrent. Surface of cushion-shaped or 

 massive sponges may bear digitate or less regularly shaped proc- 

 esses, some or all of which bear terminal oscula. Megascleres, 

 tylostyles or styles or intergrades, or a mixture of the two forms. 

 Microscleres usually present, and abundant, in the form of spirasters ; 

 frequently forming a dermal crust; sometimes exceedingly scarce 

 or even wanting. 



SPIRASTRELLA VAGABUNDA Ridley. 



Spirasirella vagabunda Ridley, 1SS4, p. 468. 

 Station D5142, three pieces. These have been sliced off from 

 what were evidently large sponges, or perhaps one sponge; the 

 largest slice measures 200 by 120 mm., with a thickness of 40 mm. 

 The elevations on the surface of the sponge are in one piece digitate 

 processes, 20-30 mm. high; in another piece the larger processes 

 are irregular nodules; in the third piece the processes are conical 

 and only about 10 mm. high. The processes contain prolongations 

 of the large canals of the interior, often a single axial canal of 

 good size in a process. .Typically, doubtless, this opens by a ter- 

 minal Osculum, but in the actual specimen open oscula are found 

 only on a few processes. The surface of the sponge is glabrous 

 and actually aporous; the pores, like most of the oscula, have doubt- 

 less closed. There are numerous large canals in the interior, 3-10 

 mm. in diameter; some sand is found here and there in the choano- 

 some. Color of sponge brown, the cortex whitish. 



