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Show 6 DR. J. S. BOWERBANK ON THE SPONGIADcE. [Jan. 7, protecting the dermal membrane from its minute enemies. These spicula are in strong contrast with the primary series of external defensive ones, which equal those of the skeleton in length and diameter. They are frequently % of an inch in length, with a diameter of 3 ^ inch, while those of the long and slender secondary series are from A- to -^ inch in length, and do not exceed ^ V o i n c n in diameter. The sponge has evidently suffered from partial decomposition, and I could not find any portion of the dermal membrane remaining in a condition for satisfactory examination; but if we may judge by the profusion of the spicula in the other membranes of the sponge, it will probably prove to be abundantly spiculous. The skeleton-fasciculi are large and strong, and especially so near the dermal surface, where strong shafts of the patento-ternate connecting spicula are incorporated with them. The latter form are very numerous and much larger and stouter than those in many other species of the genus. Their length frequently exceeds ^ inch, their greatest diameter is x-gr inch, and the expansion of their ternate radii varies from -^ to •j-f.v inch. The average dimensions of the skeleton-spicula is, length g inch, and greatest diameter -g^j inch. The recurvo-ternate spicula are also more than usually large and numerous; their slender shafts are frequently | inch in length, while their greatest diameter does not exceed Y O V O incn« The interstitial membranes are in a fine state of preservation, and are coated abundantly with sarcode; and in many parts they are literally crowded with the two forms of stellate retentive spicula, each form being about equally abundant; on some parts of the membranes they are so numerous as to render it impossible to discriminate their forms. There is another, a larger specimen of G. depressa in the Museum of the Royal College of Surgeons. In its general anatomical details it is in perfect accordance with the one described. In the larger specimen, on what was probably the upperside of the sponge, rather on one side near the thickest portion, there is an elliptical orifice five eighths of an inch long by a quarter of an inch wide, leading into an expanded cavity one and a half inch deep, in which most probably the oscula are congregated, as we find them to be in many other species of the genus. On the distal end of the sponge thelittle depressions on its surface indicating the intermarginal cavities beneath are in a good state of preservation ; and it is probable, from their forms and modes of disposition, that the pores in this species are congregated. GEODIA GIBBEROSA, Lamarck. (Plate I.) Sponge massive, sessile ; surface more or less tuberculated. Dermal membrane thin, pellucid? Connecting spicula attenuato-pa-tenti- ternate, slender. Oscula small, congregated in depressed areas in mature specimens; loosely congregated or dispersed in young specimens. Pores inconspicuous. Skeleton-spicula fusiformi- acerate, slender, and, rarely, acuate slender. Interstitial |