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Show 350 DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [May 13, Fig. 3. One of the inhalant areas on the external surface of the rigid skeleton of /. beatrix, exhibiting the elongo-conical defensive fibres and numerous verticillately spined retentive spicula in situ, X 108 linear. Fig. 4. One of the large excurrent orifices on the side of the great cloacal cavity within the sponge of /. beatrix, X 1 0 8 linear. PLATE XXII. Fig. 1. A small portion of the rigid skeleton of Iphiteon panicea from Porto Eico, exhibiting the abundance of the gemmules in some parts of the sponge, x 108 linear. Fig. 2. A portion of one of the fibres forming the oscular area of Iphiteon beatrix, exhibiting the compound reticulate nature of its structure and a few of the slender acerate spicula in situ, X 108 linear. Fig. 3. One of the attenuated rectangulated hexradiate interstitial spicula with one of the shaft-radii spinous, from /. beatrix, X-308 linear. Fig. 4. A retentive verticillately spined spiculum from I. beatrix, X308 linear. Figs. 5, 6, 7, 8. Four of the porrecto-multiradiate retentive spicula from I. beatrix, X308 linear. Fig. 0. One of the subfusiformi-cylindrical entirely spinous spicula from I. beatrix, X108 linear. Fig. 10. A portion of the surface of the rigid skeleton of Iphiteon subglobosa, exhibiting the umbonal clusters of coarso tubercles, rectangulated hexradiate interstitial spicula in situ, and numerous spinulo-quadrifurcate and pentafurcate hexradiate stellate retentive spicula dispersed amidst the interstices of the skeleton, X108 linear. Fig. 11. One of the minute spiculated biternate retentive spicula of the dermal membrano of I. subglobosa, x6f*6 linear. Fig. 12. T w o of the rectangulated hexradiate auxiliary fibres from I. subglobosa, based on a portion of a fibre of the rigid skeleton, anastomosing by their radii, X175 linear. Fig. 13. One of the pentafurcate hexradiate stellate retentive spicula of I. subglobosa, X 6 0 6 linear. PLATE XXIII. Fig. 1. A small portion of the surface of the rigid skeleton of Iphiteon Ingalli, exhibiting its confluent rotulate structure with quadrifurcate hexradiato stellate spicula amidst the fibres opposite a, a, a, a, X108 linear. Fig. 2. One of the quadrifurcate hexradiate stellate retentive spicula of /. Ingalli; three of the primary radii having been broken off, the quadrifurcate structure of the remaining radii is very distinctly displayed: X530 linear. Fig. 3. One of the rectangulated hexradiate interstitial spicula of /. Ingalli, X 108 linear. Fig. 4. A small portion of the surface of the rigid skeleton of /. callocyathes, exhibiting the more or less verticillate disposition of the minute spines of the skeleton-fibre, X 108 linear. Fig. 5. One of the rectangidated hexradiate interstitial spicula of I. callocyathes, X175 linear. Fig. 6. A furcated foliato-expando ternate connecting spiculum of I. callocyathes, covered by the minute, short, stout acerate tension-spicula of the dermal membrane, X183 linear. Fig. 7. A very perfect and beautiful example of a spinulo-multifurcate hexradiate stellate retentive spiculum of I. callocyathes, X 66G linear. Fig. 8. A view of portions of two of the intervening planes of perforated siliceous tissue parallel with the external surface of the rigid skeleton, and which divide the layers of cryptdike tissue of the skeleton of Myliusia Grayii from each other, with their numerous circular orifices of intercommunication between the upper and lower strata of the skeleton, X 1 0 8 linear. |