382 A MONOGRAPH OF THE 



arenaceous, occasionally in some parts destitute of 

 sand; sometimes tubular, or furnished with adven- 

 titious spicula of various forms, imbedded in the 

 fibre, or attached externally. Interstitial membranes 

 aspiculous. Gemmules membranous, aspiculous. 



Colour. — Alive and dried, variable, but usually dull 

 ochreous-yellovp. 



Habitat. — Coasts of Great Britain, abundantly. 

 Uxamined. — Alive and in the dried state. 



In the young state this species is occasionally found 

 thinly coating the surface of stones ; in this condition it has 

 been described by Dr. Johnston as Halichondria areolata, 

 ' History of British Sponges,' p. 121. But its usual form 

 is more or less massive, sometimes it is developed in 

 numerous short, thick, fan-like ridges, or it projects short 

 lobular branches from its surface, in an upvi^ard direction ; 

 the latter form usually occurs when it attains the height of 

 four or five inches, and which height it very rarely exceeds. 

 The asperation of the surface is produced by the projection 

 of the distal ends of the primary lines of the skeleton fibre. 

 The structure of the skeleton is so coarsely reticulated that 

 it is frequently very difficult to determine the position of 

 the oscula ; occasionally there are a few large excurrent 

 canals visible, which have their oscular terminations pro- 

 jected beyond the surface of the sponge. A few patches 

 of dermal membrane are sometimes to be found on the 

 surface, but in no case have I yet succeeded in finding the 

 pores. A few adventitious spicula may occasionally be 

 found on the dermal membrane, but it is usually free from 

 either particles of sand or spicula. The mode of construc- 

 tion of the arenaceous fibres of the skeleton is very remark- 

 able and exceedingly interesting, but as I have described 

 these structures in detail, in Vol. I, p. 78, of this work, it is 

 unnecessary to enter further into the details of their struc- 

 ture. The degree of the arenation of the skeleton fibres is 

 remarkably variable. In some cases the sponge appears 

 to consist of a mass of particles of sand, loosely cemented 



