22 ART. 9. — I. IJIMA I HEXACTINELLIDA. 



The nearly horizontal sieve-plate at the upper end is irre- 

 gularly circular, measuring 50-60 mm. in diameter. In the middle 

 it is broken ; against the lateral wall it is bounded by a low, 

 compact-looking marginal ridge. Meshes of the plate shaped as 

 in Specimen A, but on the whole somewhat larger, measuring up 

 to 4 or 5 mm. across. Beams laterally compressed, up to I mm. 

 in width as seen from above. The nodes may however be 14 mm. 

 broad. The stronger beams show a somewhat radial arrangement. 



The lateral wall is thick, measuring at places 5 mm. or over 

 in thickness. Pit-like or shallower depressions give quite an 

 uneven appearance to the external surface. The bottom of each 

 such depression is occupied by a round parietal osculum, which 

 may measure 2 mm. in diameter. The oscula are arranged irre- 

 gularly, not in regular rows. The spaces between the oscula are 

 made up of loosely connected fine fibers or ill-defined bundles of 

 fibers, which pursue an indefinitely directed and irregularly 

 flexuous course, intersecting at low angles and anastomosing in 

 all directions. Only in the uppermost portion of the wall one 

 perceives that many of the bundles show a tendency to a more 

 or less longitudinal direction. On the whole the wall, as seen 

 from the exterior, appears irregularly latticed and woolly. 



On the internal surface is seen a distinct system of rather 

 widely separated, compact-looking, wavy and intersecting bundles 

 which are in general transversely directed. 



The entire sponge is quite soft. The external surface has 

 been subjected to much laceration, but there still remains in the 

 parenchyme a large quantity of dried-up soft parts and of mi- 

 crosclene. Evidently ankylosis between the spicules nowhere exiyts 

 except in parts of the basal knobs in direct contact with the 

 substratum. 



