160 ARTHUR DBNDY. 



widely from the lines laid down by previous writers. The 

 necessity for doing so was forced upon me when preparing my 

 '' Synopsis of the Australian Calcarea Heterocoela " (4). In 

 that paper I proposed a classification of the group based upon 

 a personal examination of forty-seven species, and a careful 

 consideration of the published accounts of species which I had 

 not seen. In the Synopsis, however, I had not space to justify 

 the classification proposed, merely giving it as a skeleton upon 

 which to arrange my descriptions of species. The task of 

 justification I reserved for the present occasion, and I have 

 endeavoured to fulfil it rather by a critical re-examination 

 of the anatomy of the group than by a detailed criticism of the 

 systems of other spongologists. A great deal depends upon 

 whether one regards the canal system or the skeleton as 

 aflPording the most reliable guide to the systematist, for the 

 characters of the two certainly appear to contradict one 

 another. Here, as in similar cases, I believe that a com- 

 promise is the only satisfactory way out of the difiiculty, 

 as neither set of characters is solely reliable. The skeleton 

 evidently follows the canal system up to a certain stage of 

 organisation, and then begins to vary independently. Up to 

 this stage I believe the canal system to be most important ; 

 after it I think the skeleton has prior claims, while the canal 

 system becomes of secondary value. According to this idea, 

 which will be found elaborated later on, I regard the Leuconoid 

 type of canal system as of polyphyletic origin, as also the 

 " Sylleibid " type, and I abandon the old families Syconidse 

 (Sycones) and Leuconidse (Leucones) of Haeckel, as well 

 as the more recent Sylleibidse of von Lendeufeld. I have 

 previously shown (9) that the very generally accepted family 

 Teichonidse must be abandoned, and I am glad to see that 

 von Lendenfeld follows my lead in this (10), although he 

 declines to acknowledge any indebtedness to my writings. 



As I have naturally adopted my own classification as a 

 basis for the arrangement of the subject-matter of this paper, 

 it may be convenient to the reader if I give an outline 

 thereof at once, reserving further discussion as well as the 



