212 PALEONTOLOGY OF ILLINOIS. 



Ethmophyllum by Meek; Astylospongia, Palaeomanon and As- 

 trasospongia by Koemer; Hindia by Duncan; Pattersonia and 

 Dystactospongia by S. A. Miller; Leptomitus and Cyathophycus 

 by Walcott, Astroconia by Sollas; Cyathospongia, by Hall; 

 Lepidolites, by Ulrich; and Climacospongia, by Hinde. The 

 twelve generic groups remaining, appear to be new to science. 

 No doubt it would have enhanced the value of this report had 

 it been possible to define all of them at this time, but a lack 

 of space, but more especially, the unwillingness to describe them 

 without proper illustration, necessitated a restriction to ma- 

 terial occurring within the limits of the State, or contained in 

 the State collection. In consequence, only six of the twelve new 

 Cambrian or Lower Silurian genera are defined in the following 

 pages.* 



The Devonian and Carboniferous deposits have been much 

 less carefully searched, but the diversity of the fragments ob- 

 tained, indicate that these organisms were not less prolific in 

 those ages than in Silurian, Cambrian and Taconic times. 



A few introductory remarks upon the preservation, geological 

 distribution, and classification of palaeozoic sponges, may prove 

 of interest to students, and it is hoped that our humble efforts 

 to bring this neglected branch of our palaeozoic fauna before the 

 scientific world will stimulate other collectors to an apprecia- 

 tion of their value. 



PRESERVATION. 



The structure of the sponges of the Palaeozoic rocks, the same 

 as of those from Jurassic and Cretaceous horizons, was often 

 so much altered during the process of fossilization, that it is 

 sometimes extremely difficult to determine its original nature. 

 The mineral constituents of the spicules are apparently never 

 the same as in the recent state, though the extent of the 

 changes varies greatly. The least alteration is where the origi- 

 nally amorphous silica, or calcite, has been changed into the 

 crystalline form of these minerals. The change most frequently 

 met with consits in the substitution of crystalline calcite for 



* Since writing the above, the author has published descriptions of the other new 

 genera in the April, 1889. number of the "American Geologist." The names applied to 

 them are Havffella, Leptopoterion, Heterospongia, Saccospongia, and Cylindroccelia. 



