178 THE VOYAGE OF H.M.S. CHALLENGER. 



The parencbj-malia lying between the beams of the dictyonal framework consist of 

 small, simple, and regular oxyhexacts, with delicate, straight, and rough rays, 

 which run out with a slightly conical terminal pointing, and of discohexasters which 

 are much smaller than the oxyhexacts, but vary considerably in size and form. Some 

 of them bear on the short simple principals, three to five, rarely more, S-shaped, 

 whorled, somewhat markedly divergent, moderately thin, terminal rays with convex 

 marginally toothed transverse discs (PL CII. fig. 5). In other, usually somewhat larger 

 discohexasters of a similar type, the short simple principal rays bear six to ten long 

 terminals, which are similarly S-shaped and disposed in perianth-like fashion, only more 

 closely packed together and with less broad terminal discs (PI. CII. fig. 4) than in the 

 preceding form. Both forms are connected, however, by numerous intermediate 

 types. 



The dermalia are oxypentacts in which the straight or slightly incurved tangential 

 rays are about 0'2 mm. in length, while the straight radial proximal is twice or three times 

 as long. All the five rays are cylindrical, and are smooth except on the conically 

 pointed terminal portion. A distal tubercle sometimes appears as the rudiment of the 

 undeveloped sixth ray. The gastralia have quite the same form and an approximately 

 equal size. They are largest on the gastral surface of the body, and become smaller and 

 more weakly developed the nearer they are to the blind ends of the efierent canal system. 



Tribe II. AMPHIDISCOPHOEA, F. E. Schulze (Pis. XXVII.-LIL). 



The bounding surface-membranes always contain amphidiscs. Hexasters are wholly 

 absent from the parenchyma. There is always a tuft of basal fibres, by means of which 

 the cup- or club-shaped sponge body is rooted in the mud. The ciliated chambers are 

 not exactly thimble-shaped or sharply defined from one another, but appear rather as 

 somewhat irregular diverticula of the membrana reticularis. 



Family Hyalonematid^, Gray (Pis. XXVII.-LIL). 

 Both dermal and gastral membranes bear numerous pentact pinuli. 



Subfamily 1. Hyalonematin^, F. E. Schulze (Pis. XXVII.-L.). 



The usually cup-shaped body exhibits a more or less sharp-contoured, circular 

 oscular region, and is only exceptionally split in an ear-shaped fashion. 



