PREFACE. 



Tliis Monograph of the Dictyospongid^ is the conclusion of an under- 

 taking, the inception of which is indicated by my pul>lication upon these 

 fossils in 1884. Up to the year 1863, only occasional expressions had been made 

 Avath reference to the nature of such bodies ; first, by Mr. T. A. Conrad, after the 

 (!lose of his connection Avith the Geological Survey of the State and, again, in 

 the same year (1842), by Mr. Lardneb Vanuxem, in his final report on this 

 Survey. The specimens which came under the notice of these observers were as 

 Avidely unlike as the limits of the family permit, and while Conrad considered 

 liis specimen, Hydnoceras, a cephalopod, Vanuxem regarded the form 

 described by him, Upiiant^nia, as a marine plant. In my paper of 1 863, I was 

 disposed to accept Vanuxem's views of these bodies as nearer the truth. 



In the years which intervened, from 1863 to the date of publication of 

 my second paper, in 1884, specimens had begun to accumulate in the collec- 

 tions of the State Museum, and toward the latter part of this period especial 

 (efforts were made to gather material that Avould justify a more thorough study 

 of the subject, though little anticipating that it would ever assume the 

 comprehensive proportions with which it appears to-day. While new material 

 Avas gradually being acquired from the Chemung rocks of this State, as one 

 result of the activity of collectoi's sent out on behalf of the Palaeontology 

 of New York, additional forms were obtained from the WaAcrly sandstone 

 of Ohio, during the survey of that state by the late Dr. J. S. Newherry ; 

 and admirable specimens were being found in the calcareous shales of the 

 Keokuk group at Crawfordsville, Indiana. It was the acquisition and study 

 of this last named material, that led to the determination by Mr. R. P. 

 Whitfield, in 1881, of the spongous nature of these fossils. 



In order to show the progress which had been made in the study of these 

 organisms, I issued in 1882, four large octavo plates of figures with explana- 

 tions and, in 1884, reproduced these plates with a brief descriptive account 

 of the fossils illustrated. In 1890, an addition to the known species Avas made 

 by the publication (though without illustrations) of a group of Chemung 



