1869.] DR. J. S, BOWERBANK ON SILICEO-FIBROUS SPONGES. 347 
and 2 in breadth, which was shaken off a specimen of 4. speciosum 
that I purchased of Mr. Geale in January 1867. 
This fragment of membranous tissue is, comparatively speaking, 
of considerable thickness, and abounds in amber-coloured sarcode, 
and there appear to be two well-defined layers of tissue. In the 
external one there are numerous fasciculi of long slender acerate 
spicula, the number in each being much too numerous to be counted, 
and they are very compactly disposed. In one part of the surface 
the fasciculi radiate from a common basal point, while in two other 
parts they are nearly parallel to each other. On reversing the speci- 
men the internal layer presented a rudely cellulated appearance, 
abounding in sarcode, in which two of the most characteristic auxili- 
ary spicula of Alcyoncellum were deeply imbedded—one of them, an 
incompletely developed stout rectangulated hexradiate interstitial 
spiculum, exactly represented by fig. 181, plate 7, Mon. Brit. Spon- 
giadee, vol. i., and the other a rectangulated hexradiate one, repre- 
sented by fig. 198, plate 9, of the same work; and there is also a 
slender rectangulated hexradiate spiculum, like the one represented 
by fig. 10, Plate XXIV., illustrating the present paper. With these 
indications, I think there is little doubt that the structure I have 
described is a portion of the dermal system of Alcyoncellum, and that, 
when we obtain a specimen in the condition in which it is taken from 
the sea in the living state, we shall find the beautiful skeleton entirely 
enveloped by such a dermal membrane as I have described from the 
fragment in my possession. 
Should these ideas prove correct, a slight addition would become 
necessary in my description of the specific characters of Aleyoncellum 
speciosum in the Proc. Zool. Soc. for March 28, 1867, p. 354, line 12 
of the specific character, where the dermal membrane is described as 
“unknown,” in place of which should be added, ‘‘ Dermal membrane 
abundantly spiculous ; spicula acerate, long and slender, fasciculated ; 
fasciculi compact, disposed in radiating or parallel groups.” 
In this description of the dermal structure of the sponge, it will 
be observed that there are no connecting spicula present ; and we 
may therefore infer that the genus Alcyoncellum is not furnished 
with an expansile dermal system as in the massive rigid skeletons of 
Dactylocalyx and other similar siliceo-fibrous sponges. The fistular 
construction of the skeleton in Aleyoncellum renders such a provi- 
sion as an expansile dermal system quite as unnecessary as it would 
be in the genus Grantia and numerous other fistulous sponges. 
I obtained also two fragments of the skeleton in which there was 
a considerable quantity of sarcode; and immersed in this substance 
numerous rectangulated triradiate and rectangulated hexradiate spi- 
cula of the slender descriptions were intermixed without any apparent 
arrangement. Every one of the interstices of the fibrous skeleton, 
large or small, was abundantly supplied with them. The well- 
washed specimens of the sponge now so numerous afford no adequate 
idea of the profusion of these descriptions of spicula that exist in the 
sponge in its natural condition. 
There were also numerous indications of the presence of floricomo- 
