SILICIOUS AND HORNY SPONGES WILSON. 347 



Family POLYMASTIDAE. 



Potymastidae Vosmaer, 1887, p. 32S. 



Ectosome histologically differentiated into a cortex that is usually 

 distinctly fibrous. A cortical skeleton is also differentiated. The 

 characteristic megascleres are monactinal, tylostyles or styles, and 

 the skeleton is radiate. Ordinarily without microscleres. 



In addition to Trichostemma (see below), the genera are Poly- 

 mastia Bowerbank, 1864 (syn. Einalda, Weberella), Spinularia Gray, 

 1868 (syn. Rhaphidorus Topsent, see Stephens, 19156, p. 31), Pro- 

 teleia Ridley and Dendy, 1886 (placed by Lendenfeld, 1906, p. 175, 

 in an appendix to the Sigmatophora as a genus in which one of the 

 megasclere forms still retains a trace of its original tetraxonid 

 character) , Tylexocladus Topsent, 1898, Sphaerotylus Topsent, 1898, 

 Quasillina Norman, 1869, Ridleia Dendy, 1888, Tentorium Vosmaer, 

 1882, Atergia Stephens, 19155 (p. 32). 



Dendy, 19166, and 19216, continues as formerly to combine the 

 Polymastidae with the Suberitidae, under the latter name. But 

 the family (Polymastidae) is in general use (Topsent, 1904, 1917; 

 Wilson, 1904; Kirkpatrick, 1908; Hentschel, 1914; Stephens, 1912, 

 1915, 19156). 



Genus TRICHOSTEMMA Sars (1872). 



Trichostemma Sars, 1S72, p. 62. — Ridley and Dendy, 1887, p. 216. 

 Free living sponges of a symmetrical form which approaches the 

 hemispherical; with a marginal fringe of long radiating spicules. 

 Oscula, one or more, on only one face of the body at the ends of 

 short tubes or papillae. There is a thick ectosome so well filled with 

 spicules as to form a relatively dense cortex, which entirely surrounds 

 a much less dense choanosome. Megascleres, tylostyles varying 

 sometimes toward the style. No microscleres. 



TRICHOSTEMMA STRAT1CULATUM, new species. 



Plate 38, fig. 7 ; plate 48, fig. 1. 



Ten specimens from station D5428. 



Shape of body varying from that of a plano-convex lens to a 

 conical shape. The approximately flat face is the oscular. The 

 marginal fringe projects toward this face. The convex surface is 

 smooth and clean and in one specimen bears a slender projecting 

 process (pi. 48, fig. 1). The oscular face is covered with fine sandy 

 debris. It bears a number, 6-8, of small rounded papillae about 0.5 

 mm. in height. These are scattered, although in several specimens 

 one papilla is close to the center of the face. The papillae are 

 probably all oscular. At any rate this was found to be the case with 

 several (five) actually sectioned. Pores? 



