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



callocyathus, but which Bowerbank afterwards (1869) distinguished as Myliusia (jrayi 

 According to the label the form was found at St. Vincent, West Indies. Bowerl)arik 

 briefly characterised it^ in the following diagnosis: — " Sponge sessile, massive. Dermal 

 surface unknown. Surface of rigid skeleton uneven and excavated. Oscula, jDores, and 

 e.xpansile dermal system unknown. Skeleton stratified, forming a series of expanded 

 • lypt-like spaces. Fibre cylindrical, incipiently or minutely spinous. Interstitial spicula 

 numerous, accratc, large and long, variable in size ; disj)osed in lines at right angles to 

 the stratification in loose fasciculi of two to four or five together. Eetentive spicula 

 spiculo-multifurcate hexradiate stellate." Bowerbank also gave^ good figures of several 

 specimens. From these two figures and from preparations which I was able to make 

 during my stay in the British Museum at South Kensington, it can be distinctly seen that 

 the dictyonal framework of Aulocystis grayi differs in several particulars from Aulocy.stin 

 zittelii, Marshall. The most important difference consists in this, that on each of the 

 nodes of intersection the octahedral edges are formed not of twelve simple, cylindrical, 

 oblique buttresses, as in Aulocystis zittelii, but of twelve plates lying in the plane of the 

 two connected axes, and perforated by several round or oval smooth margined holes of 

 variable size. These plates expand to some extent in their different planes, so that in 

 some places, especially on the free bounding surfaces of tlie entire dictyonal framework, 

 conspicuous perforated siliceous membranes may be formed, as represented in one of 

 Bowerbank's figures.'' The small conical tubercles which occur all round the beams in 

 Aulocystis zittelii, are here present in abundance on the freely projecting conical bosses, 

 but elsewhere only on the edges of the perforated plates, and less abundantly, or not 

 at all on the lateral surfaces of the same. The " long acerate interstitial spicules " oi 

 Bowerbank are slender, smooth, cylindrical needles which are disposed at right angles to 

 the surface, and are in my opinion not free oxydiact parenchymalia, but the very much 

 elongated proximal radial rays of the pentact dermalia. 



Isolated pai-enchjTnalia are represented by numerous discohexasters with short 

 principal rays, varying in size and in the number, strength, and length of the terminals. 

 One of these is represented in PI. CIV. fig. 7. Besides these I frequently observed 

 bundles of those long and extremely fine terminal rays which characterise the graphio- 

 hexasters of Aulocystis zittelii. I found only a quite isolated occurrence of small simple 

 oxyhexasters. I did not observe that special form of discohexaster with medium-sized 

 principals which is so abundant in Aulocystis zittelii (PL CIV. fig. 6). 



Consequently we are led to regard Aulocystis grayi, Bowerbank, as a form nearly 

 related to Aulocystis zittelii, but yet different enough to be referred to a distinct species. 



1 Proc. Zool. Soc. Land., 1869, p. 335. 



2 Loc. cit., pi. xxiii. fig. 8, and pi. xxv. fig. 1. 

 ^ Loc. cit., pi. .xxiii. fig. 8. 



