4 DHrrYc)si>()N(Ui»:. 



81MH.-ie8, a paper prepared at ray request by Mr. John M. Clabkk. AVith this 

 pul.lication, forty-two species of these sponges had been described from the 

 pahieozoic rocks of the United States. 



So rapid lias been the growth of these collections and so generous the 

 disiMisition of all collectors and students toward the perfecting of this 

 monograph, that to-day we present descriptions of about thrice the 

 numl)er of specific fonns recognized as such, seven years ago. This 

 wonderful increase is not especially a matter for congratulation, save that it 

 serves to show the amazing diversity of these siliceous sponges in late 

 Devonian and early Carboniferous faunas. The species and genera are 

 established in accordance with the best standards attainable for these 

 variable organisms. Future collections and observations may show that these 

 divisions are not in all cases sharply defined ; they will undoubtedly show 

 that the present account of this organic element in these ancient rocks is 

 far from being complete. 



In 1892, Mr. Clarke undertook a revision of all previous work upon 

 these fossils anil this, with the elaboration of new material, he has carried 

 forward to its present state. 



During the preparation of the work, many favors have been shown by 

 geologists and others having specimens of Dictyospongidje in their collections. 

 Acknowledgments are due to them all, but our obligation to some recpiires 

 particular mention. 



Tliis monograph could never have been made what it now is, were it not 

 for the enthusiastic cooperation of Mr. Edwin B. Hall, of Wellsville, N. Y. 

 Mr. Hall has demonstrated a wonderful abundance of the Dictto 

 SP0NC4ID^E in the upper Chemung rocks of New York. His collections, which 

 are constantly growing under his zealous explorations, are remarkably rich in 

 this material and have been at all times accessible for use in this work. 

 It is to be remarked, with some regret in vie^v of the issuance of this 

 book, that Mr. Hall's more recent collections afford evidence that as yet 

 we are far fi-om having a full representation of the hexactinellid sponge fauna of 

 this geologic period, not\vithstanding that more than sixty species of 

 this ancient date are here illustrated. With our present knowledge, 

 the middle and upper beds of the Chemung group in Allegany and Catta- 

 raugus counties appear to have been the seat of extensive sponge 

 plantations, more prolific in diverse forms and individuals than the 

 region immediately to the east and Avest. This impression may, however, 

 be a mistaken one and due to the fact that Chautauipia, Chemung and 



