Repoet of the State Geologist. 



In this memoir an effort has been made to bring together all that is now 

 known concerning this remarkable family. The work is based upon the 

 result of more than fifty years of care and watchfulness in securing the mate- 

 rial which is here illustrated, and more than once during this period it has 

 seemed as if the end of these resources had been reached, but in every case 

 new forms have come to light. Explorations carried on in late years, in the 

 Chemung rocks of this State, especially by Mr. E. B. Hall, of Wellsville, 

 Allegany county, have shown a most surprising development of these 

 fossils and we have good reason to believe that, notwithstanding the fre- 

 quent occurrence of living hexactinellid sponges in existing seas, the 

 Chemung period was the time of culmination of the entire order Hexac- 

 tinellida, to which this family belongs. At the present time more than 

 seventy species of these Dictyosponges have been recognized in the Chemung 

 fauna alone, and we have been able to locate areas where they grew in 

 colonies or plantations on the sea bottom of that ancient period. In previous 

 faunas they were much fewer, and in those succeeding the Chemung, they 

 continued for only a brief period, though with most interesting manifestations 

 of form and structure. This memoir will embrace descriptions and illustra 

 tions of over one hundred and twenty species, at present recognized under 

 twenty -nine genera. 



Very respectfully, your obedient servant, 



JAMES HALL, 



State Geologist and Palaeontologist. 



