REPORT ON THE HEXACTINELLIDA. 219 



character in the tubular eflfereut canals, especially through the degeneration and final 

 disappearance of the supporting hypocanalicular pentacts, as also through the shortening 

 of the autocanalicular peutact pinuli, which further exhibit a less thickly spinose free ray 

 and longer roughened basal rays. Lastly, in the finer canals the pinuli gradually become 

 further and further distant from one another, until just before the diverticula 

 of the membrana reticularis only isolated very delicate pinuli occur (PI. XXXVI. fig. 1). 

 Numerous amphidiscs lie in the gastral-canalicular membrane, but do not penetrate as 

 far as the layer of chambers. The large form of amphidiscs (PI. XXXVI. fig. 3) is 

 here altogether absent, but the medium-sized, and especially the smaller are often present 

 in great abundance. 



The marginalia form a closed ring on the free sharp edge of the oscular aperture. 

 They have the form of moderately long oxydiacts with perfectly smooth proximal, and 

 somewhat thickly spinose distal rays. On the boundary between the two rays, two 

 opposite, or rarely four cruciate tubercles or bosses almost always project. These are 

 usually hemispherical or somewhat longer than broad, or else completely roimded off. 



The basal pad contains the familiar firm spicules with six to two rays, the ends of which 

 are beset with spines, while the inner portion remains smooth (PI. XXXV. fig. 8). The 

 strongly developed spicules of the basal tuft, almost as thick as pins, are in part smooth, 

 and in part studded with numerous nail-like barbs, which are not inserted on annular or 

 spiral cross ridges, but are disposed in isolated fashion in indistinct and: irregularly 

 developed spiral rows (PI. XXXVI. fig. 7).. Viewed from the surface, the freely pro- 

 jecting points of the teeth appear to be marked ofi" by a line of basal tubercles. Such a 

 bounding line does not really exist above, as may be readdy seen when viewed in profile, 

 but is merely the optical expression of the upper margin of the origin of the barbs on the 

 surface of the spicule. Towards the lower end the long spicules become markedly thinner, 

 the lateral barbs diverge further from one another, and the spicule ends below in a 

 peculiar hemispherical anchor sti'ucture with four double hooks cruciately disposed 

 (PL XXXVI. fig. 11), or in a hemispherical terminal knob from which four minute simple 

 cruciate pointed barbs project backwards, as in the- anchors of Hi/alonema tJwmsoni, 

 var. exiguum (PL XXXIV. fig. 16). 



Several forms of Hyalonema, difiering only in subordinate characters from that above 

 described, and whoUy agreeing with it both in general organisation and in the structure of 

 the spicules, and therefore undoubtedly belonging to the same species, were dredged in 

 the Mid-Pacific (Station 271, lat. 0° 33' S., long. 151° 34' W.) from a similar depth of 

 2425 fathoms and from a Globigerina ooze bottom. There are two perfect specimens, 

 destitute only of the freely projecting portion of the basal tuft, and also the fraginent of 

 a third form, all procured at the same locahty. All the three seem somewhat smaller 

 than the above, and exhibit either a conical form with an inferior point, or a flat cake-like 

 shape. The breadth varies from 5 to G cm; the height from 3 to 4, and in the latter form 



