40 



The entire canal-system is represented schematically in the sketch fig. 1 on 

 plate XXI. It is on the whole similar to the canal-system of the RosseUid genus 

 Aulochone, particularly Aulochone cijlindrica, described and figured by me in the 

 " Challenger" Report on the Hexactinellida on p. 168 and pi. 66, f. 2-4. 



The walls of the wide and ramified canals and diverticula of the incurrent 

 system chiefly consist of the richly-folded chamber-layer and the limiting mem- 

 branes. The membrane on the side of the incurrent system is dermal, the one 

 on the side of the excurrent system gastral. These membranes are covered with 

 pentactine canalar pinules. 



Straight or slightly-curved and slender macrosclere oxydiactines are numerous. 

 Singly, or aggregated in strands, they occupy the parenchyme of the lamellte 

 between the incurrent and excurrent systems. They extend in various directions, 

 chiefly in planes parallel to the canal surface, and on the whole resemble the corres- 

 ponding spicules of most other species of Hyalonema; they are however only rarely 

 over 1 mm. long and never attain such dimensions as the curved oxydiactines 

 in the strands of Eijalonema toxeres, rapa, martabanense and others. Some 

 of these spicules are quite smooth, others have a more or less clearly defined 

 central inflation, or two opposite or four crosswise arranged tubercles with axial 

 canals in the middle. 



I do not remember having seen any macrosclere oxyhexactines. In the 

 vicinity of the central cone, that is the upper end of the spicule-bundle forming 

 the peduncle, straight or curved, smooth diactines with thickened, club-shaped 

 ends are frequently met with. Sometimes both ends are club-shaped (pi. XXI, 

 f. 9), sometimes only one, whilst the other is gradually attenuated to the sharp- 

 pointed end. In this region also diactines are occasionally met with. These 

 are simply rounded at one or at both ends and assume the shape of styles or 

 amphistrongyles accordingly. 



Stout oxypentactine hypodermalia are frequent everywhere below the dermal 

 membrane. They take part in supporting the soft parts. Below the gastral 

 membrane no such spicules are met with. 



Microscleres, parenchymal oxyhexactines, are nowhere particularly abundant. 

 Their rays are usually 60 /^ , rarely as much as 80 ^ long, and either covered 

 with very minute spines or merely rough (pi. XXI, f. 4, 5). 



On the dermal membrane of the lower face, on the limiting membranes of 

 the internal cavities and canals, and on the inner and outer side of the gastral 

 reticulation pentactine pinules are met with. These are regularly arranged and 

 more or less numerous. They are slender and their basal rays are 40-50 t^ long, 

 smooth or slightly roughened and uniformly attenuated towards the pointed end. 

 The free main ray is 100-280 /^ and more long, and terminally covered with 

 oblique spines not particularly long. On the whole the pinules of the dermal and 



