280 PALAEONTOLOGY OF ILLINOIS. 



In sections the cribrose character of the intertwining sponge 

 leaves is quite obvious, but the component parts of the fibres 

 have been so much obscured during fossilization, that they can- 

 not now be determined. But in the matrix which fills the canal 

 cavities, a large number of minute needle-shaped bodies, as well 

 as a few three-rayed forms, were observed. 



This distinct species is separated from I), minor by the thinner 

 leaves, and much larger canals. From D. insolens Miller, the 

 type of the genus, it is distinguished by the same characters. 

 That species also presents a limited number of large radiate 

 oscula on the upper surface, which are not observable on the 

 species here described. 



Position and locality: Twenty-five feet above the base of the 

 Trenton limestone, near Dixon, 111. 



CAMAROCLADIA nov. gen. 



Sponges consisting of small subcylindrical branching stems. 

 Interior with comparatively large, but short sub-cylindrical 

 canals, or cavities, which wind about in an irregular manner 

 before opening at the surface of the branches. The canals are 

 separated by thin cribrose walls. 



The walls are now composed of crystalline calcite, and preserve 

 only very faint traces of the spicular fibre. In the canal cavi- 

 ties a number of minute, mainly isolated three-rayed forms were 

 observed. 



This genus is proposed to include small branching fossils that 

 are quite numerous in the Dixon sponge layer. In their general 

 appearance they resemble species of Buthotrephis, a genus of the 

 so-called "Fucoids." Whether any of these supposed plants are 

 really fossil Algae remains to be seen. That many are not, will 

 be shown, we think, when their obscure remains are examined 

 and studied as they should be. 



Some will probably turn out to be inorganic, others may be 

 trails and burrows, while not a few will prove to be sponges, as 

 has already been shown of Dictyophyton and Cyathophycus. 



The systematic position of Camarocladia, while not positively 

 determined, is nevertheless, sufficiently indicated by the known 

 characters, to induce us to classify the genus with the calcareous 

 sponges, in the neighborhood of Peronella and Verticillites. 



