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



is frequently very feebly developed (PI. LXXXIV. fig. 2). In addition to the uncinates, 

 the parenchyma contains hexasters of various form and most irregular distribution. 

 Sometimes one has to search long for one of these hexasters in a section, while in other 

 cases the whole preparation appears to be permeated by them. Perfectly regular 

 oxyhexasters, in which each of the principals runs out into four strong and moderately 

 long, diverging, secondary rays, are comparatively rare. Usually one finds one or more 

 principal rays terminating in simple points, while others run out into three or four ter- 

 minal rays. In another frequent form the two principal rays belonging to one axis are 

 very strongly developed, and divide into four strong, diverging terminals, while the 

 four remaining rays, which are cruciately disposed, and belong to the two other axes, run 

 out into perfectly simple points, or are only partially divided into two tei'minal rays (PI. 

 LXXXIV. fig. 7). These latter spicules seem to be related to the forms characteristic of 

 Aphrocallisies beatrix, Gray, and represented in PI. LXXXIV. figs. 9, 10, while, on the 

 other hand, small discohexasters sometimes occur, which agree in form and size with 

 certain discohexasters, which occur very frequently in Aphrocallisies vastus. These 

 have a diameter of 0"03 mm., and each of the short principal rays bears four to six 

 somewhat curved diverging terminals, each of which is tipped by a small end plate, or 

 merely by a spherical terminal knob (PI. LXXXV. figs. 8, 9). 



In regard to the soft parts, I may state that the structure of the dermal and gastral 

 membrane hardly varies from the ordinary Hexactinellid type, and the same ma}'' be 

 said of the trabecular network which extends between these two membranes and the 

 chamber layer. It is different, however, with the chamber layer itself. The most 

 important peculiarity has been already referred to in the generic diagnosis ; it claims, 

 however, more attention, especially since I was able to investigate carefully some 

 comparatively well-preserved specimens. 



In each of the honeycomb-like hexagonal spaces, which are quite open on both sides 

 in the macerated skeleton, and penetrate the wall in a radial direction, there is a peculiar 

 system of chambers, which opens on the gastral surface through a single wide round 

 aperture above the lattice-work of the gastral membrane. Into the wide, canalicular 

 space above this aperture there open laterally a number of thimble-shaped chambers of 

 medium size, in the form of simple, closely-apposed diverticula, while from the dermal 

 surface, three to five large blind diverticula also open into the same. These latter 

 diverticula closely surround the wall of the tubular skeletal space, and are laterally so 

 closely apposed to one another, that they form between them a wide, median, funnel- 

 shaped space. The inner wall of the large diverticula which surround this funnel-shaped 

 space is simply smooth, while their external wall adjacent to the surrounding skeleton 

 is distended into chamber-like diverticula, just as we previously saw on the surface of 

 the w^ide general excurrent space (PL LXXXIV. fig. 1). In this way a funnel-shaped 

 membrana reticularis is so stretched in the hexagonal honeycomb space, that the 



