REPORT ON THE HEXACTINELLIDA. 97 



in simple lacunte, which arc, for the most part, formed by a rupture of the inner tra- 

 becular framework. Wherever a hyclranth arises, the chamber layer, the outer trabecular 

 framework, and the outer wall, become perforated by a canal opening to the exterior. 



The chamber layer is but slightly folded, a circumstance which is in harmony with 

 the slight thickness of the whole body- wall. 



The principal lattice-like framework of the skeleton consists of long compact spicules 

 with a varied number of rays, but especially triacts and diacts, which, with the more 

 delicate comitalia that surround them, are, for the most part, disposed in bundles, and 

 firmly united by means of numerous synapticula (PI, X. figs. 3, G). Tlie circular beams 

 lie as before on the inner side of the longitudinal, while the oblique strands are 

 irregularly interwoven throughout the entire lattice-work. In the narrowed funnel- 

 shaped terminal portion of the sponge the spicules of the framework are more delicate, 

 shorter, and more amalgamated. 



The looser parenchymalia are in part extended spicules among which diacts seem to 

 predominate, which are provided with conical or rounded rough extremities, and in part 

 small delicate hexacts with fine transverse prickles, and lastly rosettes of two kinds. The 

 one type includes discohexasters with few, usually three, long terminal rays on each of 

 the six short principals. Where the principal ray divides an irregular tubercular 

 thickening occurs, and from this the somewhat distant, narrow, diverging terminals which 

 separate from one another project outwardly, while the extreme ends bear small discs with 

 from four to six transversely disposed, inwardly bent, thin hooks or claws (PI. X. fig. 5). 



The other rosettes are, it is true, likewise discohexasters, Init they may be distinguished 

 from those just described in difierent respects. 



The entire appearance is essentially diff'erent since, besides the stellate, the spherical 

 form also prevails (PL X. fig. 1 ; PI. XL fig. 4), on account of the great number of equally 

 long terminal rays which bear hemispherical transverse terminal discs. Each of the six 

 short principal rays passes at first into a discoid expansion, which bears on its arched 

 outer surface numerous (about thirty) terminals, which increase somewhat in strength 

 towards the exterior, and are disposed in a radiating and divergent fashion. The hemi- 

 spherical terminal discs of these terminal rays have a sharp-pronged margin which extends 

 inwards in a somewhat campanulate manner. In some cases the number of the terminal 

 rays on these rosettes is less, each principal ray bearing only about seven terminals. It is 

 noteworthy that the rosettes, which have on the whole a spherical appearance, and are pro- 

 vided with hemispherical terminal discs, always occur only in the neighbourhood of the outer 

 skin (PI. XI. fig. 4), whereas the stellate forms which are provided with transversely disposed 

 terminal tubercles are, on the other hand, scattered throughout the whole parenchyma. 



Whether the bundles of very fine rhaphide-like spicules, which I found here and there in 

 the parenchyma in the neighbourhood of the outer surface, are to be regarded as the broken 

 off terminal rays of graphiohexasters or as independent groups of spicules, I cannot 



(ZOOL. CHALL. EXP. — PAItT UII. — ISSG.) Ggg 13 



