IN THE MUD OF THE LEVANT. 25 



radiate (fig. 45.) It occurs in many living species. 

 The siliceous acicular spiculum is also abundant, 

 sometimes with one end thickened like the head 

 of a pin (fig. 47) a form which I have found in the 

 British Halichondria sulphurea {Bean's MSS) ; 

 and which also exists in Dr. Grant's sponge-like 

 Zoophyte, Cliona celata ;* at others pointed at 

 each extremity (fig. 46). The latter is the 

 most common siliceous form, and has been found 

 by Mr. Bowerbank in many of the keratose 

 sponges, from which they were believed to be 

 absent, and which were, consequently, made into 

 a separate group. Fig. 46 is not only the 

 common form amongst the Halichondriae, but has 

 been found by Mr. Bowerbank in Anthopora — 

 one of the Corallidse.f 



Two forms of spicula occur, which, probably, 

 belong to some species of Tetheia. In the fibro- 

 fleshy texture of this sponge there are bundles of 

 spicula which radiate from the centre to the 



* Found filling the holes in oyster-shells on the sea coast, 

 near Preston Pans. — Johnston's History of British Zoophytes, 

 p. 305. 



t On the Organic Tissues in the Bony Structure of the 

 Corallidse. — See page 22. 

 E 



