TRANSACTIONS. 



Art. L Description of New Species of Fossils from the Car- 

 boniferous Limestones of Indiana and Illinois, by James Hall. 



Read before the meeting of November 27th, 1856. 



The several distinct members and groups of beds of lime- 

 stone, shale, etc., constituting altogether what is usually 

 known as the " carboniferous limestone" of the Mississippi 

 valley, have not heretofore been well determined in their 

 order, extent and relations to one another. Some approxi- 

 mation to a subdivision has been made in the Report of Dr. 

 D. D. Owen, on the Chippewa Land District, and a farther 

 subdivision by Prof. Swallow, in his Report upon the Geo- 

 logy of Missouri. 



In this attempt at grouping these limestones, one of the 

 principal means of identification, that of fossils, has been the 

 great cause of confusion. One of the bryozoa (Fenestella), 

 with a solid spiral axis, known as Archimedes, has been re- 

 lied upon as the characterizing fossil ; and the term u Archi- 

 medes limestone^ has been made to include a large proportion 

 of the whole. I have found that this supposed single species 

 includes several, and that the "Archimedes" is a generic 

 rather than a specific form. I have already characterized 

 several species of this genus,* showing that they belong to 



* See Proceedings of the American Association for the Advancement' of 

 Science, 1856. 



[Trans. iv.\ 2 



