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Show 774 DR. j. s. BOWERBANK ON THE SPONGIAD^E. [NOV. 21, without contact with any other portions of its structures, the spicula of the termination radiate on the plane of the membrane like those which are projected through the dermis. This habit of terminal radiation of the fasciculi prevails in several other species of Baphio-desma. The tension-spicula are very unevenly distributed ; in some parts there are very few of them, while in others they occur dispersed in very considerable numbers. The rosette-shaped groups of dentato-palmated inequianchorate retentive spicula are rather sparingly but equably dispersed on the inner surface of the areas of the dermal network. They very closely resemble those of the type of the genus, the British species Baphio-desma lingua, both in the size of the groups and of the individual spicula of which they are constructed, but they are not nearly so numerous in each group as in the type specimen. I have never found these rosette-like groups of inequianchorate spicula in any other sponges than those of the genus Baphiodesma, and not in every species of that genus ; so that, although they cannot be considered of generic value, they are important indications of the genus whenever they are apparent. A few simple or contort bihamate retentive spicula were occasionally observed on the interstitial membranes of the skeleton ; but their number was so small as to render their presence of but little value as specific characters. The structures of the skeleton-fasciculi are longer and more continuous than in any other species of the genus with which I am familiar, so much so that the skeleton might very readily be mistaken by a hasty observation for that of a Desmacidon ; but this illusion is dissipated by the fact that they do not form a continuous network of solid fibre as in the last-named genus, but frequently terminate in radial expansions like those of the dermal membrane and its external protected groups of defensive radiating spicula. A few rosette-shaped groups of inequianchorate spicula aud a few of the bihamate ones are occasionally found on the interstitial membranes. This sponge is the only specimen of the species that I have seen; and it is a very remarkable one. By far the greater proportion of the known species of the genus are more or less of a solid massive form ; and this variation strongly illustrates the fact that there is little or no dependence to be placed on external form in regard to either generic or specific characters. EXPLANATION OF THE PLATES. PLATE LXXVIII. Desmacidon plumosa. Fig. 1 represents the sponge in its dried state, rather less than half its natural size. 2, 3. T w o small portions of the sponge, of the natural size, exhibiting the plumous nature of the hispidation of the surface. 4. T w o of the subfusiform acerate spicula of the skeleton, x 308 linear. 5. A small portion of the skeleton-structure, X 50 linear. |