400 Mr. J. S. Bowerbank on the Spongiadse, 



self that in the polypes mentioned above, the inner surfaces of the 

 polype-cells, of the appendices of those processes described in the 

 Cellularia reptans and scruposa, of the bird-head processes, of 

 the spines, and of the canals running along the lateral surfaces 

 of the polypidom in Flustra avicularis, are all lined by a fine 

 membrane. This membrane in old specimens, and when the 

 polypes are dead, often presents numerous and pretty large cells, 

 generally of a pale colour, at other times having a slightly yel- 

 lowish or brownish tinge, adhering to its free surfaces. In one 

 specimen these cells had accumulated in such quantities within 

 some of the spines in Flustra avicularis, as to produce consider- 

 able bulgings and excrescences. The growth and nutrition of the 

 hard parts of the polypidom must be chiefly due to this mem- 

 brane. 



EXPLANATION OF PLATE XIL 



Fig. 1. Magnified view of the posterior portion of the upper end of a branch 

 of the polypidom in Cellularia r&ptans. It is slightly elevated on 

 the left side, so that the polype-cells of that side are better seen 

 than on the other. 



Fig. 2. Three appendices to the cells in Cellularia rejjtans. 



Fig. 3. Magnified view of four polype-cells oi Cellularia reptans seen on the 

 anterior surface. 



Fig. 4. Magnified view of polype in Cellularia reptans when folded up in 

 its cell. 



Fig. 5. Magnified view of this polype when expanded. 



Fig. 6. Magnified view of the anterior surface of the upper part of one of 

 the branches of the polypidom in Cellularia scrupo.sa. The polype- 

 cells are in this drawing also more distinctly seen on one side than 

 on the other. 



Fig, 7. Magnified view of three appendices to the polype-cell in Cellularia 

 scruposa ; b, b, bis, views of the process bearing the hair-like pro- 

 longation in two different positions. 



Fig. 8. Greatly magnified view of head and upper part of stalk in Pedicel- 

 Una echinata. 



Fig. 9. Greatly magnified view of the ciliated ova of Pedicellina echinata. 



Fig. 10. Magnified view of polype in Crisia chelata. 



Fig. 11. Magnified view of polype-cells in Alcyonidiurn parasiticum. 



Fig. 12. Magnified view of bird-head process in Flustra avicularis. 



Fig. 13. Magnified view of ova in Flustra avicularis. 



XLIV. — Obse7'vations on the Spongiadse, with descriptions of some 

 new genera. By J. S. Bowerbank, F.R.S., L.S. &c. 



[With two Plates.] 



The microscopical examination of several hundred species of the 

 Spongiadce has led me to believe it possible that a series of cha- 

 racters may be obtained from the anatomical structure of the 

 skeleton, which, from their constancy and striking peculiarities, 

 will enable us to establish genera, based upon more certain cha- 



