56 DR. G. J. HINDE ON A NEW GENUS OF SILICEOFS SPONGES 



M. Platnauer, P.G.S., for the opportunity of studying them *. 

 Some of the specimens, from their porous aspect, had been recog- 

 nized and labelled as sponges ; but, so far as I am aware, no 

 reference to them has ever been published, and the resemblance of 

 their spicules to the detached bodies in the Calcareous Grit does not 

 seem to have been noticed. 



The specimens are now for the most part weathered out on tfie 

 surface of a hard matrix of the Calcareous Grit, consisting principally 

 of sand-grains and detached spicules like those of the sponge, 

 cemented together by calcite or silica. In one specimen the matrix 

 is decayed, so that the sponge has been quite freed from it. The 

 sponges appear to have been upright, palmate or fan-shaped, and in 

 the early stage of growth funnel-shaped in some instances 

 (PI. YI. fig. 1). No specimen is perfect; the largest individual 

 measures 140 millim. in height by 80 millim. in width, and the 

 walls are about 14 millim. in thickness. The walls consist of 

 plates or indistinct trabecuJae, which anastomose to form a laby- 

 rinthine structure (PI. YI. fig. 3). The plates are perforated irregu- 

 larly by ovate apertures or slits of varying dimensions (fig. 2), 

 ranging from 1 to 9 millim. in width ; they vary in thickness from 

 •5 millim. to 4 millim., and the interspaces between the plates of 

 the wall correspondingly vary from 1 to about 4 millim. The 

 outer surface of the wall in some cases is smooth, in others rough 

 to the touch ; occasionally small oysters are attached to it. 



These laminate walls appear to be entirely composed of the 

 small reniform or so-called globate spicules already mentioned, 

 which are closely aggregated into a solid mass, and now firmly 

 cemented together by silica resulting from the fossilization. In 

 a transverse section through the sponge-wall the spicules are seen 

 in close contact, their individual outlines for the most part being 

 clearly shown ; but in the central portions of some of the laminiie, 

 secondary crystallization has fused them into a mass of fibrous 

 chalcedony (fig. 4). The nature of these spicules can be more 

 favourably ascertained from the detached forms, obtained by dis- 

 solving some of the matrix in acid, than from those in the connected 

 skeleton, which appear to be more altered. Their mineral charac- 

 ters have already been carefully described by Dr. Sorby, and no 

 further reference needs here to be made to the circumstance that 

 some are at present of crj^stalline calcite, since it is now well esta- 

 blished that these are but replacements after silica. iSome of the 

 siliceous spicules retain outlines as smooth and perfect as in recent 

 forms (figs. 5, 6, 8, «& 10), whilst others are corroded in varying 

 degrees, small concave hollows having been scooped out from their 

 surfaces, so that they now present a very jagged appearance (fig. 9). 

 The central portion in some of the spicules also shows differently 

 tinted, banded layers of chalcedony, whilst the outer zone is 

 transparent (fig. 10). Mounted in Canada balsam they are so 



* Since my paper was sent into the Society, Mr. W. IT. Hudleston has shown 

 Die two specimens of this sponge in his own collection, one from Scarborough 

 and the other from the Coral Rug of Settriugton. 



