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Show 1873.] DR. J. S. BOWERBANK ON THE SPONGIADcE. 13 The remarkable forms of these spicula, combined with the inequicylindrical skeleton ones, render the discrimination of this species comparatively easy. The ovaria in the dermal crust are all fully developed ; but on the interstitial membranes they may be seen in all stages of development, from a size not exceeding that of one of the largest of the stellate spicula to that of the fully developed ovarium. GEODIA MEDIA, Bowerbank. (Plate II.) Sponge massive, sessile ; surface smooth. Oscula congregated in slightly depressed areas. Pores inconspicuous, congregated. Dermal membrane obsolete. Sheleton-fasciculi large, multispiculous, rather closely compacted ; spicula fusiformi-acerate, short and stout. Connecting spicula attenuato-patenti-ternate, rather short, strongly developed. Interstitial membranes-tension-spicula acerate, small and few ; retentive spicula attenuato-stellate, radii acutely conical, very variable in number, and cylindro-stellate very minute. Ovaries slightly oval, depressed. Colour in the dried state pale buff-yellow. Hab. Mexico (Mr. Thomas Ingall). Examined in the dried state. I received this sponge from my late friend Mr. Thomas Ingall, labelled Mexico. The reverse side to that figured is smooth and regularly curved, with faint parallel strise at right angles to the curve, as if it had been based on a shell with raised lines upon it or on the stem of a coral. The mass of the sponge is not perfect, portions having been broken away fiom both ends of it ; but the specimen has evidently never been much larger than it is at present. The oscula occupy two well-defined areas, which are very slightly depressed. The porous areas are visible by the aid of a lens of two inches focus ; they are not so numerous as in many other species of this genus. I could not find any remains of the dermal membrane. The skeleton is rather strongly constructed; the skeleton-fasciculi are both large and numerous. The connecting spicula are also strong and numerous ; and their shafts, incorporated with the distal ends of the skeleton-fasciculi, contribute greatly to the strength and firmness of the skeleton- structures immediately beneath the dermal crust. In their adult state the connecting spicula are large and strong, and their radii pa-tenti- ternate; but in the young and immature condition they are more or less expando-ternate, and they are found in every stage of development. There were very slight indications of the presence of recurvo-spicula. I observed among the spicula separated by nitric acid the remains of one very small specimen, and a fragment of another in one of the sections mounted in Canada balsam. The tension-spicula of the interstitial membranes are very small and few in number. The largest description of attenuato-stellate retentive spicula vary to some extent in the number of their radii; some have but three or four, while others have as many as twelve or fourteen. In the |