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Show 1875.] SILICEO-FIBROUS SPONGES. 279 smoothness of the skeleton and the well-developed system of canals in the fibres at once distinguish this species from either F. occa or F. spinulenta. It is remarkable that the sponge appears to consist of a single layer only, as I could not find the slightest trace of any other siliceo-fibrous structure on any part of the specimen. Mr. W . Saville Kent has evidently mistaken this species for Farrea occa in the description he gives of that species in the ' Microscopical Journal' for Nov. 1870, p. 248, plate lxiv. figs. 12-18; and he has correctly figured the central canals in the dermal network of his specimen (fig. 13), whereas in the corresponding organs of Farrea occa no such canals are visible. The description of the sponge represented in the same plate by fig. 12 is quite in accordance with the small fragment of the species F. lavis that I received from Mr. Lee. Mr. Kent writes, " The skeleton of this sponge is composed of a series of infundibular netted tubuli branching out from one another and occasionally coalescing." The branching fistular form represented by Mr. Kent in fig. 12, plate lxiv. ' Microscopical Journal' for Nov. 1870, occurs also in F. tubulata, very much in the shape represented by Mr. Kent; but the other specific characters differ to a very considerable extent from those of F. lavis. I received this sponge from my late friend Mr. II. Deane, along with the specimens of Farrea gassioti and pocillum ; and I presume it is from the same locality as those species. FARREA PARASITICA. Sponge parasitic, coating. Surface irregular 1 Oscula, pores, and dermal membrane unknown. Skeleton-rete irregular ; fibres depressed, occasionally confluent, very irregular in breadth ; canals distinct, variable in diameter, not always confluent, but usually so. Colour translucent as glass. Hab. West Indies (Captain Hunter, B.N.). Examined in the skeleton state. During the course of m y examination of the beautiful little specimen of Farrea gassioti, I observed on the inner surface of the sponge several small thin patches of siliceo-fibrous tissue, very much finer in structure than the skeleton of the sponge to which they were attached. On removing small portions of these tissues and mounting them in Canada balsam I found them to be strikingly different in all their specific characters from the sponge on which they reposed, and especially so in the size of their skeleton-fibres-the average diameter of those of F. gassioti being -^^s inch, while those of F. parasitica was j a W inch ; and the canals in the former species averaged 14 1 90 inch in diameter, while in the latter one their average w a s s^5 inch. These discrepancies, if there were none other, distinctly separate them as species, although iu such close contact in their natural condition. I could not, with a power of 100 linear, detect any indications of a natural dermal surface, nor could I by any means find portions of dermal or interstitial membranes or of sarcode ; our sole dependence, therefore, is upon the structural pecu- |
