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Show 222 MR. R. KIRKPATRICK ON THE PORIEERA [Mar. 6, arranged spicules. Spicules of two kinds, viz., thick, slightly curved, sparsely spined strongyles and longer, more slender, smooth strongyles. Gemmules ? Description.-Of the new species there are three small specimens in the form of thin crusts, the largest of which is 26 x 11 m m . in area and -5- 7 m m in thickness. The crusts, which have been separated from stones, still retain the curvature of the surfaces on which they grew. Their consistence is flexible and elastic, so that when they are pressed flat they immediately resume their convexity when pressure is removed. The surface is uniformly level, and in the dried condition has a glistening aspect, owing to the reflexion of the light from the tangentially disposed dermal spicules. The oscules are nearly circular, and in the specimens quite level with the surface; but probably in the perfect condition each is surrounded by a slightly raised membranous rim, since traces of such a membrane still remain on one of the oscules. Each oscule leads into a shallow basin, whence the main exhalant canals radiate out horizontally. The skeleton forms a network in which main and secondary fibres are not perceptible; the meshes (about 95 p in diameter) are irregularly triangular and polygonal, the strands being from 2-3 spicules thick. The dermal skeleton (Plate X V I . fig. 2) forms a lattice-work with triangular meshes, with strands 1-2 spicules thick formed of tangentially arranged spicules. Though the dermal layer is distinct, it is not easily separable from the parts beneath. At the base of the sponge is a well-defined lamella of spongin (Plate X V I . fig. 4), whence arise thick horny fibres with a core of one or more siliceous spicules; the fibres attain a thickness of 38u. A short distance above the basal plate the spongin disappears, and the core of spicules is continued on into the general spicular network. Spicules.-The strongyles with sparsely and finely granulated surface are 115-145 yu long and 5-6/i broad, with the ends often, but not always, slightly and gradually enlarged (Plate XVI. fig. 5); occasionally also there is a central swelling. The longer and more slender strongyles, 150-170/u X 2'75u, are smooth and taper towards the blunt rounded ends (Plate X V I. fig. 6). There are no gemmules present in the specimens. Affinities.-Although there are no gemmules present, and the megascleres are strongyles, I have placed the species in the genus Spongilla, rather than in Uruguaya (Potamolepis), because its affinities seem to be with certain species of Spongilla, viz. S. bbhmii Hilgendorf *, S.nitens Carter, and S.permixta Weltner, * Possibly Potamolepis weltneri Moore (' The Tanganyika Problem,' 1903, p. 323) may be syuonymous with Spongilla bblimii. I find the shape and size of many of the strongyles of the skeletal framework to be absolutely identical in the two species. Moore's figures (/. c. p. 323) of the spicules of P. iveltneri are not quite correct, in |