Mr. J. S. Bowerbank on a new genus of Calcareous Sponge. 299 



rays of each spiculum being disposed at right angles to the long 

 axis of the canal, while the third projects into it in a diagonal 

 direction towards the outer surface of the sponge. This arrange- 

 ment presents one of the most delicate and beautiful interlace- 

 ments of spicula that I have ever observed. Plate XVII, fig, 6. 

 represents a view of four of the cells by the aid of a Lieberkuhn 

 and a power of 100 linear. 



The large angulated canals terminate on the inner surface of the 

 sponge with open mouths, which are nearly circular and some- 

 what less in diameter than the cells, the diminution of the aper- 

 tures being produced by a greater accumulation and a closer dis- 

 position of the triradiate spicula. Plate XVII. fig. 5. represents a 

 view of a portion of the inner surface of the longer of the two 

 specimens by the aid of a Lieberkuhn and a power of 100 linear, 

 and figs. 8, 9, and 10. represent simple and triradiate spicula of 

 the outer surface of the sponge by transmitted light and a power 

 of 150 linear. 



I could not detect the passages by which the incurrent streams 

 of water pass. In most of the plates or compartments near the 

 base of the outer surface of the smaller sponge there was a cen- 

 tral depression, but I could find no perforations. The greater 

 number of the plates in the larger specimen were convex to a 

 considerable extent. 



When a piece of the sponge was placed in dilute hydrochloric 

 acid it efi*er\'esced and the spicula dissolved rapidly, leaving a 

 small mass of animal matter, from which numerous portions of 

 minute vessels projected. 



Professor Phillips in his ' Figures and Descriptions of the Pa- 

 laeozoic Fossils of Cornwall, Devon and West Somerset,^ describes 

 and figures from Sir H. de la Beche^s paper in the * Transactions 

 of the Geological Society,^ vol. iii. pi. 20, a fossil, Sphceronites 

 tessellatus, the outer surface of which has a tessellated structure 

 very similar in appearance to Dunstervillia elegans. The Professor 

 and other authors have evidently felt much doubt as to the na- 

 ture of this apparently anomalous fossil, and under this feeling 

 he concludes his observations by saying, '^ Meantime I wish to 

 include it in the group to which it bears the most obvious ex- 

 ternal resemblance, and therefore propose to name it for provi- 

 sional reference Sphmronites tessellatus.'^ 



The great similarity which exists between this fossil and Dun- 

 stervillia struck me forcibly immediately I saw the latter. The 

 external appearance of the plates or compartments in the fossil is 

 precisely that of the recent sponge, and like it, they vary in ha- 

 ving from four to six angles. In one specimen, which exhibits a 

 very complete view of the interior of the fossil, and for the loan 

 of which I am indebted to my friend Dr. Battersby of Torquay, 



