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



curvature towards tlie dermal surface. The lateral union of these longitudinal radial 

 plates, which are separated by spaces of uniform breadth, is effected by means of trans- 

 verse bridges of the same dictyonal framework. These extend uniformly on the gastral 

 side, where they are perforated only here and there by long oval openings, while similar 

 bridges arching over the interradial spaces on the dermal side have a more limited longi- 

 tudinal extension. In this manner a canal system is formed, which is, for the most ])art, 

 hmoitudinally disposed, and is here and there dichotomously branched. It opens towards 

 the outside by somewhat long longitudinal clefts, towards the inside by round or oval pores ; 

 and since the inner openings are frequently arched over by the external connecting 

 bridges of the adjoining radial plates, it often results that a transverse section of a com- 

 plete tube exhibits the appearance of a folded plate (PI. XCIV. fig. 3 ; PI. XCV. fig. 1). 

 The beams of the fibrous framework bear small superficial knobs, which are either 

 irregularly scattered or arranged in incomplete transverse rows (PI. XCV. fig. 2). The 

 nodes of intersection are somewhat thickened and knobbed here and there, especially in 

 the outer layer of the framework. 



On the outer (dermal) surface the dermal membrane extends quite uninterruptedly 

 over all the clefts and openings, while on the inner surface the gastral membrane passes 

 into the excurrent openings of the larger efferent canals, which in most cases traverse the 

 wall vevy obliquely. 



The strong dermal pentacts almost invariably exhibit a button-, peg-, or knob-like 

 rudiment of a sixth distal ray. The proximal ray, which varies in length, and the four 

 tolerably long, and in most cases slightly curved tangential rays, terminate in points 

 and are beset with small conical knobs all over in the case of the larger spicules, but 

 only on the extremities of the, rays in the smaller (younger) forms. Strong scopulaj' 

 also occur, in which the four parallel or slightly diverging, thick or slender, rough 

 knobbed terminal rays usually arise just above an annular quadri-tuberculate thickening 

 of the stalk (PI. XCIV. fig. 8). 



Finely pointed slim oxydiacts extend here and there in bundles, close to the proximal 

 ray of many dermal pentacts, in the dermal membrane, and even above the latter. 



The gastral skeleton almost completely resembles the dermal. A distinction could 

 only be found in the fact that the pentacts are less strong, and their projecting rudiment 

 of the sixth ray is somewhat longer, so as almost to warrant the term hexact. The 

 gastral scopulae agree completely with the dermal. 



The parenchjnoia contains delicate uncinates, and numerous isolated, thin-pointed 

 spicules, which are united in somewhat loose bundles. Besides small hexacts of 

 various dimensions and provided with small terminal knobs (PI. XCV. figs. 3, 4), 

 sphjerohexasters occur. These have a variable number of curved terminal rays, which 

 are in most cases only of medium size, and are convex externally (PI. XCIV. figs. 6, 7, 



1 The scopulse figured on PI. XCIV. figs. 5, 9, do not belong to this form. They are casual intruders. 



