KEPORT ON THE HEXACTINELLIDA. 151 



1. Bathydorus fimbriatus, n. sp. (PL LVIIL). 



In the North Pacific, at Stations 241 and 248, and from considerable depths, the 

 trawl brought up fragments of a somewhat large, bladder-shaped sponge, which was 

 found to be a Hexactinellid of the very simplest structure. 



At Station 248, lat. 37° 41' N., long. 177° 4' W., from a depth of 2900 fathoms 

 and a red clay ground, the somewhat injured, though coherent upper portion of a bladder- 

 shaped sponge was trawled. The loose smooth wall is only 1 to 1*5 mm. in thickness, 

 and becomes gradually thinner towards the sharp oscular margin, which is surrounded 

 by a fringe of long diact marginalia. The diameter of the bag, which is almost cylin- 

 drical in its lower region, measured from 4 '5 to 5 cm. The lumen is gradually narrowed 

 towards the upper end, measuring only 2'5 cm. in diameter at the superior terminal 

 opening (PI. LVIIL fig. l). The almost uniformly smooth external surface exhibits 

 minute, regularly distributed, round holes, of about \ mm. in diameter. Somewhat 

 larger round openings may be detected on the internal surface of the gastral membrane, 

 which is also almost uniformly smooth. 



An inspection of flattened portions of the wall, or better still, an examination of cross 

 sections at right angles through the wall, reveals distinctly the thimble-like form 

 of the ciliated chambers, which are disposed in a very simple and regularly folded layer 

 between the two reticulate limiting membranes, and supported by the external subdermal 

 and internal subgastral trabecular framework. From the larger, lacunar, subdermal 

 spaces, duct-like diverticula pass between the externally arched folds of the chamber 

 layer. The lumen of each of these cupola-like folds is free from the trabecular scaffold- 

 ing, and opens into the lacunar subgastral spaces; the latter do not, however, open 

 directly into the general gastral cavity, but only into the loose meshwork of the gastral 

 membrane which stretches smoothly over them (PI. LVIIL fig. 2). 



The larger parenchymalia consist of slender diacts which vary in length, and do not 

 exceed 0'08 mm. in thickness. They are rough and rounded off at their ends, and are 

 frequently somewhat club-shaped in consequence of thickening. A central swelling or forma- 

 tion of tubercles, which take the form of four cruciate, or two opposite elevations, is present 

 in many cases and absent in others. Between these long supporting spicules, which are 

 almost always disposed quite, or approximately parallel to the surface, numerous oxy- 

 hexasters occur, _,with a variable number of long terminal rays, which are either straight 

 or gently curved (PL LVIIL figs. 4, 7). This curvature of the long terminal rays 

 frequently assumes an S-shaped form, and results in the formation of minute, delicate, 

 three or four-rayed perianth-like whorls at the end of the principal rays (PL LVIIL fig. 7). 



The dermal skeleton is supported by medium-sized, smooth, hypodermal ox}q)entacts, 

 in which the four tangential rays, intersecting at right angles, lie close below the dermal 

 membrane, and are opposed to the corresponding tangentials of adjacent pentacts to 



