DENDY-HOMOSOLEROPHORA AND ASTROTETRAXONIDA 227 



I refrain from publishing a reference list of literature with the present instalment, 

 as it will be quite sufficient to publish one list later on for the whole of the Tetraxonida. 

 In the meantime the dates given after authors' names may afford sufficient clue to the 

 memoirs referred to. 



Order TETRAXONIDA Dendy [1905]. 



Sponges with siliceous spicules whose fundamental form is tetraxonid and tetracti- 

 nellid. (This fundamental form is often obscured by secondary modifications, and the 

 spicules may even disappear completely in some degenerate forms.) 



In 1905 I proposed to arrange the order Tetraxonida as follows : — 



Grade Tetractinellida. 



Sub-order Homosclerophora. 

 „ Astrophora. 



,, Sigmatophora. 



Grade Lithistida. 

 Grade Monaxonellida. 

 Sub-order Astromonaxonellida. 

 „ Sigmatomonaxonellida. 



The Sub-orders Astrophora and Sigmatophora were, of course, adopted from SoUas 

 [1888] and the Homosclerophora replaced his Microsclerophora. 



The Astromonaxonellida were regarded as being derived from the tetractinellid 

 Astrophora and the Sigmatomonaxonellida from the tetractinellid Sigmatophora [Dendy, 

 1905, p. 133]. 



The views thus expressed as to the phylogeny of the Tetraxonida have been accepted 

 by Hentschel [1909, 1911 a] in his work on the Tetraxonida of S.W. Australia. He has, 

 however, proposed a modification of my arrangement which gives clearer expression to 

 these views and which I gladly accept. He divides the order Tetraxonida directly into 

 three sub-orders :— - 



Sub-order 1. Homosclerophora Dendy. 



,, 2. Astrotetraxonida Hentschel ( = Astrophora -f- Astromonaxonellida 



Dendy). 

 „ 3. Sigmatotetraxonida Hentschel ( = Sigmatophora + Sigmatomonaxo- 



nellida Dendy). 



We are thus, I hope, finally rid of the old artificial distinction between " Tetracti- 

 nellida" and " Monaxonida," introduced by Zittel [1878 a], which the "Challenger" 

 Reports unfortunately did so much to emphasise. 



With regard to the Lithistida and Ceratosa Hentschel remains in some doubt, 

 suggesting that they may have to be added as two separate sub-orders to the three 

 above mentioned. This is possibly the best thing to do with the Lithistida in the 

 present stage of our knowledge, though I should not like to commit myself to a definite 



29—2 



