440 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



obliquely upward and are digitate or spinous in shape, up to about 

 5 mm. long and 1.5-2 mm. in diameter. Branches 1.5-2 mm. thick; 

 thin or often membranous between the ridges. The mode of growth 

 is obviously such that the free processes become confluent, then con- 

 stituting ridges of a lamellate branch. 



It is, however, only in places, chiefly in terminal (younger) parts 

 of the sponge, that independent branches exist. Elsewhere the 

 branches have for the most part fused edgewise to form a tubular 

 structure, 10-25 mm. in diameter, which itself exhibits irregular 

 branching. The inner surface of the tubes is smooth or nearly so, 

 while the outer bears the above-mentioned processes and ridges, the 

 latter in some specimens assuming a very meandriform aspect. The 

 wall of the tube retains the thickness of the original branches and, 

 like the latter, shows many membranous areas (fenestrae). The 

 cavities in the several parts of the tubular structure are by no means 

 all confluent. Some are, but many cavities are isolated as a result 

 of their mode of formation. The cavities open to the exterior above 

 and sometimes below and laterally. 



One specimen shows that after the tubular structure has been at- 

 tained the formation of conspicuous digitate or spinous processes 

 and independent lamellate branches may be practically suppressed, 

 the tubes growing in direct and simple fashion. That is, the whole 

 sponge is in this case tubular, the inner surface smooth, the outer 

 adorned with many meandering ridges and low processes, the wall 

 fenestrated with many membranous areas. 



The more or less tubular sponge may grow predominantly in one 

 direction, or in several directions, the largest specimens measuring 

 110-120 mm. in greatest length. The attachments indicate that the 

 habit is in general repent. The sponge is somewhat compressible 

 but firm; color in alcohol, a very light brown. The membranous 

 fenestrae show better after drying. 



Pores in the meshes of the dermal reticulum. Doubtless very 

 small scattered apertures are the oscula. 



The skeletal reticulum of spiculo-fibers is close with rounded or 

 elongated meshes. Main fibers longitudinal, 80-120 \l thick, the in- 

 cluded styles forming a core surrounded by abundant spongin; the 

 included styles belong both to the stout and slender skeletal forms. 

 These fibers are less than the length of a skeletal style apart. Con- 

 nectives like main fibers but in general slenderer with fewer rows 

 of spicules. 



/Spicules. — 1. Skeletal styles, (a) Stout form, smooth, slightly 

 curved, 180 by 10 \l to 250 b}^ 12 \l. (h) Slender form of about same 

 length but only 6 \l or thereabouts in thickness. 



