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Show 76 DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. [Jan. 28, When the expansile dermal system is present wholly or in part in specimens under examination, we are enabled to establish specific characters of external form and structural peculiarities of the most satisfactory description ; but when that important portion of the organic structure of the sponge is absent, the characters derived from the form and surface of the rigid skeleton are necessarily provisional, and can maintain their places in its description only until a specimen in a natural and perfect state can be procured. Wheu in the denuded state, the form and surface of the sponge should be stated as those of the rigid skeleton, not as that of the sponge. Genera. DACTYLOCALYX, Stutchbury. Skeleton siliceo-fibrous. Fibres solid, cylindrical. Reticulations unsymmetrical. Type Dactylocalyx pumiceus, Stutchbury, P. Z. S. 1841, p. 86. IPHITEON, Valenciennes. Skeleton siliceo-fibrous. Fibres solid, cylindrical. Reticulations symmetrical. Areas rotulate, confluent. Type Iphiteon panicea, Museum Jardin des Plantes, Paris, from Porto Rico, 1799. M Y L I U S I A , Gray. Skeleton siliceo-fibrous. Fibres solid, cylindrical. Rete symmetrical, disposed in a series of crypt-like layers parallel with the external surface, with intervening planes of perforated siliceous tissue. Type Myliusia callocyathes, Gray, from the Island of St. Vincent, P. Z. S. 1859, p. 439, and 1867, p. 506. KALIAPSIS, Bowerbank. Skeleton siliceo-fibrous. Basal fibres cylindrical and canaliculated ; distal fibres non-canaliculated, compressed. Basal reticulations symmetrical and reversedly arcuate; distal reticulations unsymmetrical and continuously ramifying. Type Kaliapsis cidaris, Bowerbank. FARREA, Bowerbank. Skeleton siliceo-fibrous. Fibres canaliculated, canals continuous. Rete symmetrical; interstices rectangulated. Type Farrea occa, Bowerbank. PURISIPHONIA, Bowerbank. Skeleton siliceo-fibrous. Fibres canaliculated, canals continuous. Rete unsymmetrical. Type Purisiphonia Clarkei, Bowerbank. |