OCR Text |
Show 322 DR. J. S. BOWERBANK ON THE SPONGIADcE. [Mar. 18, drical. Interstitial membranes-spicula the same as those of the dermis, comparatively iew in number. Colour, dried, light ochreous yellow. Hab. Nichol Bay, Australia (Mr. George Clifton). Examined in the dried state. This remarkable specimen of Dictyocylindrus is 17\ inches in height, and its greatest breadth 7 inches; the branches appear all to have maintained their natural position, and several of them near the distal termination of the sponge are united by inosculation. The natural base has been preserved. The pedicel is stout and short, and it does not rise from the base quite 3 inches before it is resolved into numerous ascending branches, which divide dichoto-mously or trichotomously. Each of the branches is furnished with •aumerous stout compressed tooth-shaped processes, consisting of converging compressed masses of skeleton-spicula pullulating from the axial skeleton of the branch, and entirely enveloped by the coriaceous dermis. The most decisive specific character of this sponge is undoubtedly the singular forms of spicula that abound in the dermal membrane, the dentato-cylindro-hexradiate defensive and retentive spicula. The membrane is crowded with them in all parts. From the shortness of their radii allowing them to assume any imaginable position, when mounted for examination their normal form is not always to be readily recognized ; but a careful observation soon establishes the true nature of their structure. In nearly all of them the number of the dental terminations of the radii vary; but the tridentate terminations appear mostly to predominate. Abnormal variations in the forms of these spicula are by no means infrequent. The axial skeleton of the branches fills the whole of their diameter, and has all the characters of a true Dictyocylindrus. It is rather compactly constructed; and a few slender spicula, of the same form as those of the skeleton, are interwoven at various angles with those of the great ascending column. The true structure of this sponge can be exhibited only in a longitudinal section. ECIONEMIA ACERVUS, Bowerbank. (Plate XXX.) Sponge massive, pedicelled (?) ; surface even, minutely hispid. Oscula simple, dispersed, few in number. Pores inconspicuous. Dermal membrane furnished abundantly with subtuberculated fusi-formi- cylindrical spicula, very minute and short. Connecting-spicula attenuato-expando-ternate, large, stout, and abundant, aud with a considerable number of attenuato-recurvo-ternate spicula; shafts long, slender, and attenuated. Skeleton-spicula of axis fusiformi-acerate, very large and stout. Interstitial membranes-tension-spicula acerate, minute, and slender, numerous, and tuberculated fusiformi-cylin-drical, short and stout, very minute, numerous. Retentive spicula subsphero-attenuato-stellate; radii few and very slender, and cylindro-sphero- stellate radii short and numerous ; both forms very minute. Colour in the dried state dark brown. |