OF THE SPONGIAD^. 173 



EciONEMiA, Bowerbank. 



Sponge. Having a strong axial column or centre of closely 

 packed siliceous spicula disposed in lines parallel to 

 the long axis of the sponge, from which axial column 

 or centre a peripheral system of spicula radiates at 

 about right angles. Distal ends of the radii furnished 

 more or less with ternate connecting spicula, the 

 radii of which are disposed immediately beneath the 

 dermal membrane. 



Type, Ecionemia acervus, Bowerbank, MS. 



This genus differs from Bictyocylindrus in having the 

 axial column composed of a dense mass of parallel spicula 

 instead of a column formed of an open network of spicula ; 

 and the peripheral system is also different, inasmuch as it 

 is essentially a portion of the interstitial system of the 

 sponge, and not more especially a defensive system as it 

 appears in Bictyocylindrus ; in no species of which genus 

 has there ever yet been found ternate spicula at the 

 surface, while in Ecionemia acervus, the type species of 

 the genus, they are abundant. 



The structure of the peripheral system exhibits a close 

 alliance with the genera Pachymatisma and Tethea. Ecio- 

 nemia differs from Geodia and Pachymatisma in the total 

 absence of the siliceous ovaries, and of the crustular dermal 

 coat formed principally of those bodies in the last-named 

 genera. There are also no cylindrical valvular inter- 

 marginal cavities, and the ternate apices of the connecting 

 spicula appear always to be applied to the inner surface of 

 the dermal membrane. This arrangement of the tissues 

 therefore forms a natural transition from Pachymatisma to 

 Tethea, in some species of which genus the ternate spicula 

 are found without the dermal membrane in the porrecto- 

 ternate form, and are adapted to defensive purposes, while 

 in others they occur immediately beneath it as patento- 

 temate connecting spicula. I have therefore assigned this 

 genus a position between Pachymatisma and Bictyocylin- 



