OCR Text |
Show 16 DR. J. S. BOWERBANK ON THE SPONGIADcE. [Jan. 7, larger specimen ; while in T. cranium they are extremely abundant, but much more minute than those of T. simillima. I found but one description of gemmule in T. simillima, which was very similar in form and structure to the larger form that exists in T. cranium; and in these organs we again find a considerable difference in the proportions of the spicula of the two species. In T. cranium the porrecto- ternate spiculum of the gemmule is more slender in its general proportions, and the radii are expanded at a greater angle and are much longer than those of T. simillima. The unihamate spicula also exhibit a characteristic variation in form. In T. cranium the hamate apex is more clavate but the hook less produced than in T. simillima ; in the latter the hook is not only very strongly produced, but the spiculum often becomes bihamate ; and a practised eye would readily distinguish the one species from the other by these characters alone. Thus, although very closely allied in their general structure, there appears to exist a sufficient permanent structural difference to warrant our considering them distinct species. TETHEA CLIITONI, Bowerbank. (Plate III.) Sponge spherical, slightly depressed, sessile. Surface even, smooth, minutely pitted or areolated, areola very shallow. Oscula and pores inconspicuous. Dermal rind thick and very solid, exterior and interior surfaces furnished with a thick stratum of large closely packed sphero-stellate spicula; radii acutely conical; interspaces with comparatively few of the large sphero-stellate spicula, but abundantly supplied with minute subsphero-stellate spicula with clavate cylindrical radii, variable in form and size. Dermal membrane aspiculous. Skeleton-radial fasciculi poly spiculous; fasciculi compact, expanding slightly towards the dermal surface, through which their distal terminations pass, to a slight extent forming external defences ; spicula fusiformi-acuate, rarely cylindrical, or fusiformi-acerate, large and long. Interstitial membranes-retentive spicula the same as those of the dermal rind, few in number. Sarcode dense. Colour in the dried state light orange. Hab. Fremantle, Australia (Mr. G. Clifton). Examined in the dried state. The form of this sponge is that of a slightly depressed sphere. Its greatest horizontal diameter is 13 lines, and its height 11 lines. Its location is especiallyremarkable. It is seated on the top of a mass of agglutinated sand and mussel-shells; and, apparently feeling the insecurity of its situation, it has given off from its base seven root-like basal processes, two of which divide shortly after leaving the sponge and proceed in different directions: the longest of these appendages is 1*| inch, and its greatest diameter rather exceeding a line; it terminates in an irregularly formed adherent expansion about 3 lines in diameter. These root-like appendages form no part of the specific character of the sponge ; they are projected, in accordance with the necessities of the individual, by almost every species of Tethea with which I am acquainted. |