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Show 1869.] DR. J. S. BOWERBANK ON SILICEO-FIBROUS SPONGES. 333 attenuated to a sharp point. In size, compared with those I have previously described in a fragment of the membranous tissue, they are small and slender. The genera of the two sponges /. Ingalli and Dactylocalyx pumiceus being distinctly different, it is unnecessary to enter into a long description of their differential characters to prove that Dr. Gray is in error in assigning the type specimen of the former to the latter genus; but it may be as well to state that none of the singular and beautiful forms of spicula which I have obtained from the type specimen of D. pumiceus, and have figured in Plate III., part 1, are to be found in the tissues of the type specimen of I. Ingalli. IPHITEON CALLOCYATHES, Bowerbank. Myliusia callocyathes, Gray, P. Z. S. 1859, p. 439, Radiata, pl. xvi. Sponge sessile or slightly pedicelled, cyathiform. Upper surface of rigid skeleton even ; under surface sinuously plicated and tubulated. Oscula and pores unknown. Expansile dermal system-dermal membrane pellucid, furnished abundantly with minute short, stout, acerate tension-spicula ; connecting spicula furcated foliato-expando-ternate. Skeleton-fibre variable in diameter, verticillately spinous, spines small, acutely conical; interstitial spicula rectangulated hexradiate, axial and rectangulating radii nearly equal in length, slender, terminations subclavate ; retentive spicula spinulo-multifurcate hexradiate stellate, terminations of each heptaradiate or octoradiate; of two sorts, one with terminal radii expanded, the other with terminal radii contracted into separate groups. Colour in the natural state unknown. Hab. West Indies (Dr. M'Gee). Examined in the skeleton-state. In the description of the external characters of this sponge it must be remembered that it is that of the rigid skeleton only, and that it is probable that both surfaces would be more or less smooth and even when covered by the expansile dermal system. The arrangement of the skeleton is decidedly that of an Iphiteon ; but the structural character of the fibres of which it is composed is strikingly distinct from any other species of the genus. They are variable in size to a considerable extent; but whatever may be their diameters, they are always furnished with numerous small sharply conical spines, which exhibit a strong tendency to a verticillate arrangement ; and around the central umbones of the confluent areas of the skeleton they are frequently congregated on slightly elevated detached patches, each containing from seven to ten minute spinules. These structural characters would have sufficed, in the present state of our knowledge of the species of this genus, to distinguish it from any other member of the group; but, by a careful examination of the type specimen, I fortunately obtained from near the base of the sponge on the inner surface a small piece of the expansile dermal system in connexion with a portion of the surface of |
