No. VI.— REPOET ON THE HOMOSCLEROPHORA AND ASTROTETRAXONIDA 

 COLLECTED BY H.M.S. "SEALARK" IN THE INDIAN OCEAN. 



By Arthur Dendy, D.Sc, F.R.S., F.L.S., Professor of Zoology in the 

 University of London [King's College). 



(Plates 44—48.) 



Read 17th June, 1915. 



The present instalment of my Report on the Sponges collected in the Indian Ocean 

 by the " Sealark " expedition deals with a portion only of the Tetraxonida, viz. the 

 Homosclerophora and Astrotetraxonida, leaving the Sigmatotetraxonida — a very large 

 group — to be dealt with subsequently. It will be noticed that the families Spiras- 

 trellidee and Latrunculiidee, hitherto included by general consent in the Astrotetraxonida, 

 are omitted from the present communication. The reason for this is that I have con- 

 vinced myself — largely through investigation of the " Sealark " material — that the 

 so-called asters of these two families are really pseudasters, and that the groups in 

 question are of desmacidonid origin and must therefore be included amongst the 

 Sigmatotetraxonida. I hope to discuss the question at length in a future instalment of 

 my Report. 



The classification of the Astrotetraxonida is as yet by no means in a satisfactory 

 condition, but a comprehensive revision of the group will be necessary before attempting 

 any radical reform. Such a revision I have already commenced in conjunction with my 

 colleague Mr R. W. H. Row, but it would not be desirable to delay the publication of 

 this report until it is completed, as it must necessarily take a long time. I may be 

 allowed to state, however, that, although I retain the family Pachastrellidse as a matter 

 of convenience, I cannot regard that family, as generally understood, as constituting 

 a natural group — it probably contains forms on the up-grade from the Homosclerophora to 

 the Stellettidse and others which are nothing but degenerate Stellettids. The latter 

 appear to be analogous to the so-called "Epipolasidae," but differing from these in that 

 it is only the rhabdome of the trigene that has undergone reduction. The " Epipolasidse " 

 I no longer accept as a family, those which are present in the " Sealark " collection wiU be 

 found amongst the Stellettidse. 



SECOND SERIES— ZOOLOGY, VOL. XVII. • 29 



