^[. K. A. Zittel on Fossil Hexactmellida. 415 



complete state to my collaborateurs. It is true that there were 

 greater difficulties in the way of obtaining the material for a 

 thorough investigation of fossil sponges than I had anticipated ; 

 for in general these fossils could only boast of having attracted 

 but little attention. In consequence of this circumstance 

 large complete collections are still wanting ; even in the 

 richest museums, as a rule, only particular localities are repre- 

 sented in a satisfactory manner. Through the great kindness 

 of many friends *, however, I have already succeeded in 

 obtaining, not only from Germany and Bohemia a great 

 number of the species described by Goldfuss, Miinster, F. 

 Homer, Reuss, Geinitz, Schliiter, F. A. Romer, and others, 

 partly in typical original specimens, partly in specimens 

 which were furnished with authentic determinations by the 

 authors, but I also obtained abundant material for com- 

 parison from Russia and England through the kindness of 

 M. F. Schmidt of St. Petersburg, Prof. Sinzow of Odessa, 

 M. Constantine Milaschewitsch of Moscow, and Mr. John 

 Edward Lee of Torquay. For the communication of recent 

 Hexactinellida and Lithistida my special thanks are due to 

 Dr. W. Marshall of Weimar, and Dr. H. J. Carter of Bud- 

 leigh-Salterton. 



The following attempt at a system of the Hexactinellida 

 has not proceeded from a desire to transform the existing clas- 

 sifications at any cost ; but when the microscopic method of 

 examination which has already proved so admirable in the 

 case of the recent Hexactinellida had been also extended to 

 the fossil sponges, so many new facts and points of view came 

 to light that of necessity more or less profound modifications 

 became requisite in the previous attempts at classification 

 both of the recent and fossil Hexactinellida. 



Revision of the Fossil and Recent Hexactinellida^ arranged 

 according to their Relationships. 



Class SPO^^GI^. 

 Order HEXACTINELLIDA, 0. Schmidt. 

 Siliceous sponges with spicules of sexradiate form, isolated 



♦ I hasten here to express publicly my thanks to those gentlemen who 

 in the mcjst liberal manner placed materials for my investinration at my 

 disposal. I have especially to offer my tliaiiks to MM. K. Andrse of 

 Bonn, E. Beyrich of Berlin, W. Dames of Berlin, Theodor Fuchs of 

 Vienna, W. Giimbel of Miuiich, II. B. Geinitz of Dresden, J. Krenner i>f 

 Pesth, Ottnier of Brunswick, F. Romor of Breslau, H. Homer of Hildes- 

 heim, A. Schlonbach of Salzfjitter, C. Schliiter of Bonn, K. von Seebach 

 uf Gijttingen, and G. Tschermak of Vienna. 



