THE SPONGES. 101 



Poecillastra Soiias. 



1888. Poecillastra Sollas, 1888, p. 79. 



1894. Poecillastra Sollas, Topseut, 1894, p. 383. 



1894. Pac/iastrella pars Leudenfeld, 1894, p. 94. 



1902. Poecillastra Sollas, Topseut, 1902, p. 10. 



1903. Pachastrella {Pachastrella') O. Sclim. j)ars + Pachastrella 



{Nethea') pars + Sphinctrella 0. Schm. pars Lendenfeld, 

 1903, pp. 70, 73, 78. 



Poecillastra tricornis, sp. nov. 



Plate 13, Figs. 13-14; Plate 14, Figs. 1-8. 



Diagnosis. Body plate-like. One surface somewhat convex, and bearing the pores. 

 Opposite surface somewhat concave, and bearing the oscula. Main afferent and efferent 

 canals similar ; numerous and small ; radial to corresponding surface ; of the uniporal 

 type, the aperture of the canal (pore or osculum) lying in the centre of a circular mem- 

 branous area, and provided with a strong chone-like sphincter. Megascleres. Oyea. 

 Triaene, with degenerate rhabdome (triod), chiefly ectosomal, but also in the interior. 

 Hicroscleres. Microxea, annulated, 400-500 ix long. Microxea, nearly smooth, 120 fx long. 

 Spiraster, dermal ; spicule length, 20 fx ; rays, 2-3 fx long. Metaster and spiraster, paren- 

 chymal; intergrading and very similar; spicule length, 20-26 /a; rays, 7-8 fx long. 



Station S404i one large specimen and two fragments. 



The larger specimen is a plate 100 mm. wide, and in general 5 mm. thick, 

 Fig. 8, Plate 14. The free edge of the sponge describes about a semi- 

 circle. Along the remaining part of its periphery the plate has been 

 broken across, probably not far from the line of attachment. In this 

 region the plate is thicker than elsewhere, attaining a thickness of 10 mm. 

 The plate is not quite flat, but is slightly folded, so as to produce wide, 

 shallow depressions on both surfaces. One surface, designated the oscular 

 surface, is throughout the peripheral region slightly concave, meeting the 

 free margin of the sponge along a sharp boundary line. The opposite 

 surface, designated the pore surface, is throughout the peripheral region 

 slightly convex, and is evenly rounded off at the margin. 



The color is whitish-brown, the consistency firm, the surface almost hard. 

 Both surfaces of the sponge are smooth, save for a few scattered oxeas, 

 which project radially or obliquely 2 to 20 mm. On both surfaces, beneath 

 the dermal membrane, the tangentially placed spicules supporting it are 

 partially visible. 



The two surfaces of the sponge are much alike, both exhibiting, scat- 

 tered evenly over the whole face, circular shallow depressions, each of 

 which is lined by a smooth membrane pierced in the centre by a single 



