NOTICE. 



Double insertions corrected (from synonymy chiefly). The localities attributed to both insertions are to 

 be placed under the species retained. Some recent acquisitions are added. 



* Twentieth Eegents' Eeport, New York, 1868. 



P.S. These Corrections will add to the accuracy of the Specific Numerical Relations although the difference 

 made is only 1-4 per cent, on the whole Silurian life. The double insertions are useful to beginners. 



