PREFACE 



No comprehensive study of the fossils of the Mississippian formations 

 of Illinois and the adjacent parts of the Mississippi Valley Basin has ever 

 been attempted. The species have been described in various publications, 

 in state reports, in short papers in the transactions of learned societies, 

 geological journals, etc.; many forms have never been illustrated, and 

 many still remain undescribed. The literature on the subject is widely 

 scattered, and most of it is not readily accessible to a large number of 

 geological workers and students. James Hall's Report on the Paleontol- 

 ogy of Iowa, published in 1858 and long since out of print, still remains 

 the principal source of information to most students, concerning these 

 faunas. 



The present work is a start towards the preparation of a series of 

 monographs which it is hoped may eventually cover all the groups of 

 organisms whose fossil remains are preserved in these formations. The 

 brachiopods have been selected as the first group to receive consideration 

 because of their almost universal presence in the faunas, and because their 

 characters are such as to make them most readily recognizable under 

 ordinary conditions. The specimens are much more apt to be preserved 

 in a sufficiently complete condition to allow of their identification, than 

 are the specimens of some other groups, such as the crinoids for instance. 

 They are much more abundant than are the species of the several classes 

 of Mollusca, and they do not require the grinding of thin sections, as do 

 many of the Bryozoa. Furthermore the species are almost all rather 

 closely limited in their geological range, being characteristic for the most 

 part, of the fauna in which they occur. The field geologist who has the 

 means at hand to enable him to recognize the brachiopods will not have 

 difficulty in determining the horizon of the strata he may be studying. 



In the present work all the brachiopods known to occur in the forma- 

 tions of the standard Mississippian section of the Mississippi Valley, so 

 far as they could be secured, have been considered. These formations 

 have their typical development not alone in Illinois, but also in Missouri 

 and Iowa, so that not a few of the examples studied, described, and illus- 

 trated are from localities outside of Illinois, although most of the species 

 may be looked for in the Illinois formations. A few forms from adjacent 

 regions, Indiana, Kentucky, Arkansas, and southwestern Missouri have 

 been included in the discussion of the species and perhaps may never be 

 found in any Illinois locality ; the reason for their inclusion here being 

 their relationship to Illinois species. 



