202 ADDITIONS AND CORRECTIONS. 



crusted surface of this sponge I also observed numerous round 

 siliceous molecules which were dispersed amid the spicula of 

 that part in great abundance. The diameters of these in many 

 cases were equal to that of the surrounding spicula, but the 

 greater number did not exceed the half or a third of that size." 

 — Boiverhank. 



In Figure 3 of Plate' V. are shown the simple and stellate spi- 

 cula, and the gemmules of this remarkable sponge. A very 

 beautiful drawing of it, and of its parts highly magnified, has 

 been made for Mr Bowerbank, to illustrate a paper which my 

 friend is about to publish. Mr Bowerbank inclines to consider 

 the species as the type of a new genus, — an opinion in which I 

 concur. It may be considered as standing between the genera 

 Halichondria and Geodia, to narrow the gap that kept them 

 so widely asunder. The bodies which Mr Bowerbank has de- 

 scribed as the gemmules of its crust are, he writes me, very 

 much alike in structure to the granules of the Geodia, which 

 he finds also occur in the body of this sponge, as well as in the 

 crust. This suggests the query — whether the cuticular gra- 

 nules of Geodia may not be truly gemmules ? but I confess 

 that to me it appears the question should be answered in the ne- 

 gative. Their position, their siliceous and crystalline character, 

 and the mode of their aggregation, seem all opposed to it ; and 

 not less so, the difference between them and the recognized gem- 

 jnules of some Halichondrias. 



