SILICIOUS AND HORNY SPONGES WILSON. 469 



the most part rounded and simple, but sometimes pointed and some- 

 times bifid. They may approach the rosette type (found in Leio- 

 dermatium pfei 'ferae, for instance), in that on and around a simple 

 rounded tubercle, simple or bifid pointed processes are formed, as 

 is indicated in one of Dendy's figures (pi. 4. fig. 2c). Developing 

 desmas are abundant beneath the dermal membrane. 



A point not mentioned in the description of the type is the radiate 

 arrangement of the fenestrae (alveoli) of the skeletal framework. 

 This is very marked in sections of the cleaned skeleton even to the 

 unaided eye. the fenestrae appearing as rounded or squarish spaces, 

 often about 200 p. in diameter, arranged in rows that are radial to 

 the margin of the vase mouth and obliquely radial to the two sur- 

 faces. The intervening skeletal beams are mostly 100-200 \i thick. 



In the type the oxeas are said to form "loose wisps or brushes, 

 running at right angles to the surface, beyond which their ends 

 project," disappearing more or less completely from the deeper parts 

 of the sponge. The largest complete spicule measured reached 

 only 1.88 mm. by 8 p.. The Albatross specimen seems to present a 

 difference in this matter, for the oxeas are in compact and closely 

 set bundles, often as thick as 100 t/,, although sometimes much 

 thinner. The bundles project, where the surface has not been rubbed, 

 about 5 mm. The appearance is very much as in Microsclerodernia 

 hirsuturn Kirkpatrick (Kirkpatrick, 1902, pi. 4, fig. 15). The con- 

 stituent oxeas vary greatly in size but reach a length of 10 mm. with 

 a thickness of 40 y.. 



The sigmas are 6-8 \k long, as compared with 10 [x for the type; 

 otherwise there is agreement. 



The type is from the Gulf of Manaar. Dendy (19215, p. 7) has 

 recently described specimens from the Indian Ocean. 



******* 



Representatives of five of the nine recognized families are de- 

 scribed above. The remaining four families, listed and in part 

 discussed below, are not represented among the sponges studied. 



Family NEOPELTIDAE. 



Xeopeltidae Sollas, 18SS, p. 344. — Lexdexfeld, 1903, p. 140. 



Family SIPHONIDIIDAE. 



Kii>honi(lii(lae Lendenfeld, 1903, p. 140. 

 Cladopeltidae Sollas, 1888, p. 317. 



In this family (Siphonidiidae) since Lendenfeld's synopsis there 

 have been recorded the following species: Siphonidium ramosum (O. 

 Schmidt), Topsent, 1904, p. 63; Plakidium (new genus) acufatm, 

 new species, Lendenfeld, 1906, p. 360. 



