OF THE SPONGIAD^. 207 



considerably in the structural characters of their skeletons, 

 which consist of a somewhat irregular radiation of primary 

 fibres from the base towards the apex of the sponge, with 

 an unsymmetrical series of secondary fibres emanating 

 from and connecting together the series of primary ones. 



The primary fibres are compressed and broad in their 

 form, frequently three or four times the width of the 

 diameter of the surrounding cylindrical secondary ones. 

 But their most striking character is their possessing a con- 

 siderable number of siliceous spicula, which are irregularly 

 imbedded in their centres ; sometimes the series of spicula 

 within the fibre consists of but one or two beside each 

 other, and at other times they are numerous and very 

 irregularly disposed. This central series of spicula appears 

 to exist only in the primary fibres, and I have never been 

 able to detect the slightest indication of their presence in 

 any of the secondary series. I first described these 

 structural peculiarities in a paper read before the Micro- 

 scopical Society of London, January 27, 1841, and it is 

 published in vol. i,- p. 32, plate iii of their ' Transactions.' 



I have met with numerous instances of the occurrence of 

 this structural arrangement of the skeleton in sponges from 

 Australia and the Mediterranean, but their well-washed 

 condition has left them with but very few capabilities for 

 specific distinction. 



I propose to adopt De Blainville's name, Halispongia, 

 to designate this genus, the characters of which are as 

 follows : 



Halispongia, De Blainville. 



Skeleton kerato-fibrous. Fibres solid ; primary fibres com- 

 pressed, containing an irregularly disposed series of 

 spicula. Secondary series of fibres unsymmetrical, 

 cylindrical, without spicula. 

 Fig. 278, Plate XXXVI; represents one of the large 



primary keratose fibres containing siliceous spicula, and the 



irregular system of small aspiculous keratose fibres, X 175 



inear. 



