298 Mr. J. S. Bowerbank on a neiv genus of Calcareous Sponge. 



one of our oldest geological strata^ to which I believe I shall 

 hereafter prove it to be very closely allied. 



I possess but two specimens of the recent species ; one of them 

 is attached by a broad base to the stem of a Corallina, the other 

 was found detached^ but appears to have been based in a similar 

 manner ; so far therefore as I can judge from this limited num- 

 ber, the sponge is a sessile species. Plate XYII. figs. 1 and 3. 

 represent them of the natm'al size. 



Both of them present the same compressed character, the elon- 

 gated one to a greater extent of the two ; and this compression, 

 it is evident from the mode of disposition and the proportions of 

 the radiating canals, is natm-al, and not the effect of collapse 

 from drpng. 



The ventral orifice in the larger specimen is nearly closed, and 

 in the smaller one entu*ely so, by a thick fringe of long, attenuated, 

 asbestiform spicula, which converge towards a point opposite the 

 centre of the orifice ; surrounding the base of this terminal fringe 

 there is a second thin fringe of similar spicula based upon a ring 

 slightly raised from the sm'face of the sponge. The latter radiate 

 at nearly right angles from the surface of the animal ; but as 

 these appendages have evidently suffered much from mutilation, 

 it may be that the second one is but the outer portion of one 

 mass of spicula surrounding the great excurrent orifice. 



The external surface of the sponge is composed of polygonal 

 plates or compartments, visually four-, five- or six-sided, as repre- 

 sented by Plate XVII. fig. 3. vn.i\i a power of forty-five linear, 

 and also by fig. 4. with a Imear power of ninety-four. In many 

 parts of the surface they present the appearance of a quincuncial 

 arrangement. 



Upon examining a section of one of these plates or compart- 

 ments made at right angles to the natural surfaces, the outer 

 portion was found to be composed of a layer of minute, simple- 

 double-pointed spicula, with then* axes at right angles to the 

 outer sui'face of the plate ; and immediately beneath these there 

 is a mass of large triradiate spicula, many of which have one 

 ray much exceeding in length either of the other two ; and this 

 occurs more especially when they are in the neighbourhood of 

 the under sm-face of the layer of simple spicula, and in these 

 cases the long ray is usually imbedded amid the simple spicula 

 of the outer layer. Plate XVII. fig. 7. represents a portion of a 

 section of one of the plates, \'iewed by transmitted light, with a 

 power of 150 linear. 



Beneath each of these plates or compartments there is a single 

 large angulated canal, usually four- sided, which passes in a straight 

 line towards the central axis of the sponge. The parietes of these 

 canals are composed of interlacing triradiate spicula, two of the 



