OCR Text |
Show 1874.] DR. J. S. BOWERBANK ON THE SPONGIADJE. 301 labelled " Mexico." It is firmly based on the remains of the stem of a fucus. The surface, to the unassisted eye, has a minutely reticulated appearance, arising from the closely disposed and exceedingly numerous porous depressions; but in the living state it would most probably be quite smooth. The oscula were congregated in an irregular group near the basal attachment ; they are simple in structure and very small, the largest of them scarcely a line in diameter. The internal structure is remarkable for the abundant varieties of its spicula. The skeleton-fasciculi are composed of numerous, somewhat slender, fusiformi-acerate spicula; and the fasciculi are very much strengthened near the surface of the sponge by the incorporation in their substance of the shafts of the numerous connecting spicula, those of the patento-ternate ones frequently being nearly twice the diameter of those of the skeleton and considerably longer ; both the patento-ternate and the recurvo-ternate ones are numerous; but the porrecto-ternate forms are of rare occurrence and are frequently very slender. The interstitial membranes are abundantly supplied with the two forms of retentive spicula, and especially so with the smallest of the two forms. A fully developed one, of the largest size, measured T W I T m c h extreme diameter; and two of the smaller description were ^oVd m c n and T2T¥ m ( m m diameter; and the latter one was not the smallest one in the field of view. The radii of the largest form were always acutely terminated, while those of smaller ones were truncated or slightly expanded at their distal terminations. The retentive spicula are very characteristic of the species, from their minuteness and great abundance on the interstitial membranes; while, on the contrary, the tension-spicula are comparatively of rare occurrence. The ovaria are abundantly dispersed on all parts of the interstitial membranes in various stages of development. HALISPONGIA VENTRICULOIDES, Bowerbank. (Plate XLVI1. figs. 1 & 2.) Sponges from Otaheite, Ellis and Solander's Natural History of Zoophytes, p. 206, tab. 59. figs. 1, 2, 3. Spongia otahitica, Esper, vol. ii. tab. of Sponges lxi. (copied from Ellis and Solander). Sponge cup- or fan-shaped, thin ; pedicle short and stout. Surface rather prominently ridged or mammillated in lines radiating from the base to the distal margin, ridges or mammae more or less elongated, margin of cup thick and rounded. Dermis retiform ; rete abundantly arenulous. Oscula simple, minute, dispersed, few in number. Pores inconspicuous. Skeleton-primary fibres abundantly arenulous ; secondary fibres rarely arenulous. Colour in the dried state ochreous yellow. Hab. South Sea, Otaheite. Examined in the dried state. The prevailing form of this species is the cup-shaped one, subject to a considerable amount of variation. The specimen represented by |