OCR Text |
Show 1875.] SILICEO-FIBROUS SPONGES. 507 In m y description of A. speciosum, in P. Z. S., May 13, 1869, p. 346, I described a small fragment of what was probably the dermal membrane of the sponge, beneath which the elaborate and beautiful defensive arrangement of spicula described in this paper would be situated. The account of this little fragment foreshadows the description of the investing animal tissues of the sponge described by the correspondent from the ' Challenger,' quoted above. FARREA VALIDA, Bowerbank. (Plate LVII. figs. 1 & 2.) Sponge-mass unknown. Dermis furnished with a stout, quadrilateral, smooth or, rarely, slightly tuberculated siliceo-fibrous network, armed at the angles externally and internally with short, stout, imbricated, conical spicular defences; areas square or slightly oblong, very regular, sides of the areas abundantly armed with rectangulated sexradiate defensive organs; radii spinous; spines acutely conical; fibres of the dermal rete cylindrical, very stout, equable in size, canaliculated; canals regular, strongly produced, confluent at the angles. Skeleton-rete quadrangular, areas larger than those of the dermal network. Fibre smooth, not more than one third the diameter of those of the dermis; canals large and well developed. Dermal membrane obsolete. Colour, in the dried state, dark amber-brown. Hab. Unknown. Examined in the dried state. All that I know of this sponge is a piece of the dermal network a quarter of an inch in length by one eighth of an inch in breadth. It is mounted in Canada balsam. Beneath the dermal rete there is a small portion of the true skeleton-rete in situ. The specific characters derivable from the dermal structures are remarkably striking. The fibres of the dermal structure are comparatively very large; their average diameter measured - ^ inch, while those of the true skeleton averaged ^4-o m c a onty> au(l tl>e central canals in both measured sAtrff inch. The fibres of the dermal structure are spineless ; but there are occasionally a few low rounded tubercles dispersed on their surfaces. The mode of the reticulation is exceedingly regular ; and the areas are all square or, to a slight extent, oblong, slightly curved at the angles. The conical spicular defensive organs at the angles are short, but very stout, and the imbricated scales are strongly produced. The most strikingly distinctive characters are the numerous rectangulated sexradiate defensive organs, based on the dermal fibres, and projected into the areas frequently to the extent of half their breadth. Their number is very considerable; and four or five are not uncommon in a single area. They vary in size and form to a very considerable extent, some being exceedingly stout, and abundantly and strongly spinous, while others are slender and delicately spinous. All these organs appear to be furnished with a central canal; but it is frequently rendered indistinct by the profusion of spines on the surface of the organ. The small portion of the true skeleton does not present |