with descriptions of some new genera. 409 



Haversian canals. In the sponge, these minute radiating canals 

 are also present, but they are much fewer in number, and re- 

 quire a power of 1000 linear to render them distinctly apparent. 

 Under these circumstances they are seen, as represented in PI. 

 XIV. fig. 6, radiating from the oat-shaped cavities, and usually 

 decreasing in diameter until they terminate at unequal distances 

 from the parent cavity, in exceedingly minute points. In many 

 cases, the commencement of these minute canals is expanded in 

 the form of a funnel, so as beneath a power of about 500 linear 

 to cause the oat-shaped cavities to appear fringed with a series 

 of projecting points. 



The surface of the fibre is covered with nucleated cytoblasts 

 and tessellated cellular structure in various stages of development, 

 and in the centre of some of the more fully-developed of these 

 cells, in place of their being entirely filled up by the secretion of 

 cartilaginous matter, there is frequently an elongated cavity re- 

 maining, which probably becomes one of these peculiar organs, 

 after having been immersed in the cartilaginous substance of the 

 fibre by successive layers of cellular structure. Occasionally, but 

 by no means frequently, there are small patches of ramifying ca- 

 nals situated immediately beneath the surface of the fibre, as re- 

 presented at PI. XIV. fig. 7 a, as seen with a linear power of 100. 

 It is difficult to imagine what office these canals perform in the 

 (economy of the animal, as they do not appear with the same de- 

 gree of constancy or regularity as in other sponges where similar 

 tissues occur in like situations. 



In some of the expanded portions of the fibre, there are often 

 small round or oval holes, and around these the oat-shaped cavi- 

 ties are arranged in a series of concentric rings, exactly repre- 

 senting the mode of arrangement of the corresponding organs in 

 true bone, in the vicinity of the Haversian canals. 



It is much to be regretted that there are no remains whatever 

 of spicula or of fleshy interstitial substance to be found in this 

 interesting specimen, nor am I aware of the part of the world of 

 which it is a native, as it was procured from a dealer in natural 

 curiosities, who could afford no clue to its previous history. The 

 specific characters, therefore, must be considered as provisionally 

 given, until other specimens may be found from which fuller and 

 better characters may be established. 



The form of the sponge is that of a thick disc, the diameter 

 being five and a quarter inches, and the thickness, one inch and 

 three quarters. The two broad surfaces correspond exactly in 

 form and structure ; a portion of one of them is represented by 

 PL XIV. fig. 8. 



There is no appear?iiicc, at any part of the sponge, of a point 

 of attachment or base. 



Ann. ^ Mag, N, Hist. Volx\u 2G 



