332 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



membrane causing the appearance of "pore areas." The canals 

 are less than 1 mm. in diameter and 1-2 mm. apart (pi. 48, fig. 3). 



The oscula vary in diameter from 2 mm. to less than 1 mm., and 

 are very abundant, commonly about 3 mm. apart. Two or three, 

 occasionally more, oscula may open into a common shallow surface 

 depression, or they may open singly. Round each osculum there 

 is a narrow depressed marginal zone which is perforated by small 

 apertures resembling pores. Where the oscula open into a common 

 depression, the whole floor of this between and around the oscula 

 is porous. The main efferent canals opening at the oscula are radial 

 to the surface and something less than 1 mm. in diameter (pi. 48, 

 fig. 3). 



The sponge is comparatively dense and compact, whitish brown 

 in color. 



The skeleton of the interior is made up of oxeas of very different 

 sizes, many of them large; thickly and irregularly strewn. Vague 

 tracts of spicules are here and there distinguishable, extending from 

 the interior toward the surface. There is a very little spongin unit- 

 ing the spicules, best seen in teased preparations on spicules that 

 have been torn apart. 



The ectosomal skeleton at each surface of the sponge is distinct, 

 although it shades off into the choanosomal skeleton. At the pore 

 surface are well defined radiating brushes of oxeas, thickly and uni- 

 formly distributed, and projecting slightly beyond the surface. The 

 skeleton of this surface also includes multispicular tangential tracts 

 of oxeas, lying between the pores, but these are obscured by the 

 radiating brushes which are about 400 jjl long. 



The ectosomal skeleton of the oscular surface in general is com- 

 posed of tangent i ally placed oxeas. These form a dense, smooth 

 dermal crust about 100 [X thick. The porous areas round the oscula, 

 on the contrary, have the same kind of skeleton as the pore surface 

 of the sponge. 



Spicules. — 1. Choanosomal oxeas, 140 by 7 to 1,350 by 32 [x, the 

 larger sizes abundant. The spicule is smooth, slightly curved, and 

 tapers gradually from the middle to the points, which are sharp. 



2. Ectosomal oxeas similar to those of choanosome, but smaller, 

 ranging from 140 by 7 to 450 by 16 \l. The oxea is not infrequently 

 represented by a style. 



3. Trichodragmas, in the choanosome: not very abundant. The 

 exceedingly fine hair-like spicules may occur singly but usually in 

 bundles, about 100 by 2-8 p, including from 2 or 3 to a considerable 

 number of spicules. The spicules of a bundle are often loose and 

 divergent at the ends. The trichodragmas arc frequently curved, 

 sometimes spirally, round two or three of the larger megascleres, as 

 if holding them together. They are best seen in teased preparations. 



