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Show 1873.] DR. J. S. BOWERBANK ON THE SPONGIADcE. 5 The largest description of stellate retentive spicula vary greatly in their size and degree of development, and also in the number of their radii. In some there are little or no indications of a spherical central mass, and the number of radii does not exceed six or eight, while others have well-developed central spheres and very numerous radii. The small stellate retentive spicula are very much more numerous than the larger ones, and they all appear to have well-developed spherical centres. The extreme diameter of an average-sized one measured -^^yrj inch ; and a smaller one did not exceed -^fao" inch. The average greatest diameter of the larger description of stellate retentive spicula was *n>Vcrlucn' The ovaria do not exhibit any important specific characters. I have dedicated this species in memory of the veteran naturalist the late Dr. Fleming, who has worked so much and so ably to extend our knowledge of British natural history, and to whom we are indebted for the first detailed description of a British Geodia, under the title of Cgdonium Miilleri, in his 'History of British Animals,' p. 515. GEODIA DEPRESSA, Bowerbank. (Plate I.) Sponge massive, sessile ; surface minutely hispid, even. Oscula congregated in depressed areas, numerous, small. Pores inconspicuous, congregated? Skeleton-fasciculi large; spicula fusiformi-acerate, large and long. Connecting spicula attenuato-patento-temate, large and long, and recurvo-ternate, radii stout, shafts long and slender. Interstitial membranes abundantly spiculous; retentive spicula attenuato-stellate, large and very numerous, and cylindro-sphero-stel-late, small and very numerous. Ovaria spherical, slightly depressed. Colour in the dried state cream-white. Hab. Dardanelles (J. T. Streatfield, Esq.), Museum of Royal College of Surgeons, B. 181. Examined in the dried state. This sponge is in size and form very like an irregularly compressed Normandy pippin, its largest diameter being two and three quarters, and its greatest height an inch and three quarters. Its original attachment is at the thinnest part of its circumference, where there is a small univalve shell about a quarter of an inch in length imbedded, with a portion of a bivalve, apparently a Mytilus, attached to it; but other than these substances there are no appearances of attachment, and it had probably been freely floating about in the sea for a considerable period before it was taken. On that which is apparently its upperside, closely adjoining the shells above named, there is an irregularly oval depression an inch and half in length and about a quarter of an inch deep, in which the numerous small oscula are congregated, and surrounding which there is a thick crop of large and long fusiformi-acerate external defensive spicula ; and the remains of similar spicula may be detected on other parts ot its surface. Beside these large spicula, there is a secondary set of external defensive ones, which are very long and slender, projecting through the dermal surface for about one-third or one-fourth of their length, and |