SILICIOUS AND HORNY SPONGES WILSON. 461 



it : fairly abundant, but distributed singly at distinct intervals. The 

 spicules are oxeas, 300-350 by 1-2 tx. They doubtless correspond to 

 the orthotrichites observed by Sollas (1888, p. 307) in boiled out 

 preparations. 



The dermal crust formed by the mierostrongyles is one layer deep. 

 The spicules have the characteristic wavy (angularly serpentine) 

 shape and measure 21-32 by 4-5 \i. 



The streptasters are 20-24 pi long; axis short, slightly curved, 

 sometimes appearing to be straight ; the rays, tapering and sharp- 

 pointed, commonly both on the axis and at the ends. The spicule 

 varies, as in Sollas' specimen, from forms with shorter and more 

 numerous rays to those with longer and fewer, frequently 5-8, rays. 

 The amphiaster shape, with about 3 rays at each end, is sometimes 

 assumed. 



Family PLEROMIDAE. 



PJeromidac Sollas. 1SSS. p. 312. 

 Pleromatidae Lexdenfeld. 1903, p. 140. 



With special ectosomal megascleres having the form of triaenes. 

 Desma monocrepid and not tuberculate, sometimes of a simple rod- 

 like character. 



COSTIFER, new genus. 



Desmas typically rodlike, without clads; loosely articulated to- 

 gether. Other megascleres are ectosomal plagiotriaenes, large oxeas 

 radial to the surface, and small parenchymal oxeas. Microscleres, 

 streptasters and microrhabds. 



COSTIFER VASIFORMIS, new species. 



Plate 43, fig. G; plate 50, figs. 8, 13, 14; plate 51. fig. 1. 



Station D5168, one specimen, dried. 



A vase-shaped sponge 270 mm. high; transverse diameters of 

 upper end, 280 mm. and 210 mm.; base flattened and about 150 mm. 

 wide. The cloacal cavity extends throughout the sponge and is, 

 no doubt accidentally, open below. Wall of vase 20-25 mm. thick 

 in the upper part of sponge, thicker below. Sponge heavy, firm and 

 incompressible, but scarcely stony. Color, light brown to light gray. 



Outer surface of sponge much incrusted with foreign matter. 

 Naturally it is covered with a crust of projecting plagiotriaenes. 

 Closely set fine canals, 0.25-0.5 mm. in diameter, extend in from 

 this surface, their apertures more or less covered by the layer of 

 plagiotriaenes. The surface of the cloacal cavity shows closely set, 

 rounded apertures, 1 mm. and less in diameter; these doubtless 

 are small oscula. 



