824 W. J. SOLIAS ON THE STRUCTURE AND 



Note, October 1877. 



It may not be out of place if I indicate here the kind of plan 

 which I have set myself to follow in making a study of the fossil 

 sponges. First, then, I wished to begin by publishing as exhaus- 

 tive a description as I could of a number of single species of fossil 

 sponges, each to illustrate a well-marked structural type, and 

 having done this, to determine how far the various existing fossil 

 species could be referred to these previously ascertained types. 



The first part of my plan is now nearly accomplished ; descrip- 

 tions of Stauronema, Pharetrospongia, and Siphonia have appeared 

 to illustrate the Vitreohexactinelridae, BenieridaB, and Lithistidae 

 respectively ; while we may expect to be furnished shortly with a 

 good example of the Sarcohexactinellidae (Acanthaspongia, Hyalo- 

 nema) by other observers. The abundant material which has been 

 placed at my disposal by the great kindness of Mr. Woodward at 

 the British Museum, and by Mr. Moore of the Liverpool Free Mu- 

 seum, has now given me the opportunity of proceeding with the 

 second part of my plan, i. e. with the classification of the various 

 fossil species. Already I find that the Lithistidae are well repre- 

 sented in the fossil state by very numerous species of great diversity 

 in form and structure ; Miss Benett's forms, for instance, more nearly 

 related than I had previously imagined, belong all, or nearly all of 

 them, to various Lithistid genera, some having affinities to Discoder- 

 mia, some to Macandrewia, and others presenting us with a new 

 generic type. No less abundant are the fossil Renieridse, all the 

 sponges with reticulate calcareous skeletons from Faringdon, such 

 as Manon macropora, Jerea mutabilis, Scyphia foraminosa, and 

 others, belonging to this group, or being closely allied to it. The 

 Hexactinellidse have already been dealt with in a very full and 

 complete manner by Professor Zittel. 



Hitherto the fossil sponges have furnished me with no type which 

 does not find its close representative in existing seas. The existence 

 of extinct calcareous sponges with reticulate skeletons finds no sup- 

 port from a study of either fossil or recent sponges ; it is the merest 

 myth ; and the classification of D'Orbigny and his successors, based on 

 an assumption, may now be regarded as finally and completely disposed 

 of. I had the honour to receive a separate copy of Professor Zittel's 

 Monograph on the fossil Hexactinellidae on the day after this paper 

 was read. Our independent observations agree in a manner no 

 less remarkable than satisfactory, due doubtless to our having 

 both followed the same modern methods of research. The points of 

 difference between us are but few. Thus Professor Zittel speaks of 

 the existence of fossil calcareous sponges with a reticulate fibrous 

 skeleton ; but I have reason to believe that since the publication of 

 my paper on Pharetrospongia he has abandoned all belief in such 

 forms, and thus made criticism on this matter needless. Professor 

 Zittel also seems to consider that I regard the genus Stromatopora 

 as belonging wholly to the Hexactinellidaa : this has at no time 

 been my view ; I regard the genus Stromatopora as a heterogeneous 



